A family trip in an RV. Perfect. Oh, really?

Back in my single days, I spent two weeks hiking in the Grand Canyon and had been wanting to share the experience with my wife and two-year-old daughter - especially since we have family in Phoenix, only four hours away.

But I wanted them to see it right, not just drive up and back in a day. A ranger had explained on my earlier trip that the average tourist's visit to the Grand Canyon lasts only three hours.

If you count waiting in traffic and looking for parking, that leaves about 15 minutes to look over the edge.

That's the problem with the Grand Canyon: Looking out over the top, it's so incomprehensibly vast that the mind flattens it into a two-dimensional painting. Achieving a sense of scale requires a few days trekking, or at least driving around.

But how to get our proposed group of four adults and three children under four years old to the canyon for that long without going nuts - and everyone still on speaking terms at the end?

Clearly, with little ones in tow, tent camping would be no vacation.

But staying in a hotel smacked of keeping nature at arm's length in a room that feels like Anywhere USA.

So we chose a middle road - that most-American travel machine, the motor home - to spend two days and nights at the canyon.

It sounded so simple: Rent an RV and go anywhere, any time. If somewhere you're staying doesn't live up to expectations, just check out someplace else down the road. You don't even need a campground in which to spend the night.

Unfortunately, the reality wasn't so smooth.

The first shock came even before we arrived in Arizona. Calling the RV dealer as we waited to board a plane in Minneapolis, the news on the other end of the line was grim.

The "magic carpet" we had reserved wouldn't be ready when we arrived in Phoenix in three hours. The vehicle wasn't even in Arizona, so there was no guarantee when it might be ready.

This was Saturday and our Monday canyon trek couldn't be postponed because my brother-in-law couldn't reschedule his vacation.

A few phone calls after landing in Phoenix, and we had Plan B: The RV dealer would pull a new unit out of his inventory, prep it that afternoon, and let us take it the next day.

That was the theory anyway.

I arrived at the dealership early Sunday morning to find a giant motor home jacked up in the service bay.

Prepping 37 feet of RV, with all its different systems - diesel fuel, propane, two septic tanks, water heater, furnace, and three air conditioners, among them - took most of the day. Teaching me how to use each of them took the rest.

There's a lot to remember: Instructions for setting up and breaking camp filled pages of notes. And the box of owner's manuals was more than 12 inches high.

But Monday morning we were ready to go - except for one problem: The air-pressure gauge was supposed to read 120 pounds, and it was sitting at 80 pounds. This mattered, because air pressure works the brakes. A little fiddling with the controls and restarting the engine did the trick, and we were off.

There were seven of us: my daughter, my wife, her brother and sister, the sister's two kids, and me. Not to mention scads of baby gear and bags of toys.

Interstate 17 runs north from Phoenix towards the canyon. As any map will tell you, north is up, and in this case that meant a grade cresting over 8,000 feet just before our lunch stop in Flagstaff, Ariz. That may sound like a nonissue in a car. But in a 26,350-pound RV, it's not so simple.

We didn't make it. At least not for a while.

As we pulled up the final grade, a screaming buzzer was accompanied by an orange light on the dash reading "water temp."

I pulled off the road for 20 minutes to let the engine cool down, so as not to do real damage.

The problem never recurred, so we'll never know if it was a false alarm.

Meanwhile, we learned the hazard lights were also dysfunctional.

After lunch and $50 worth of diesel fuel, we headed out on US 180, a narrow, two-lane highway in what felt like a two-lane-wide bus.

Driving a truck with a chassis by Freightliner and a huge Caterpillar diesel engine is every boy's childhood dream.

In reality though, this 10-ton RV felt like driving a house.

Oh, don't get me wrong. It had lots of fascinating technology to try out. And the view of the road was terrific - a bulky Ford Explorer looked like a speck below the windshield.

Traffic lanes offered little room to spare, however. Just keeping the RV between the lines was a constant effort, with clearance barely a foot on either side. On rural, two-lane highways, it can be a matter of inches.

Still, that wasn't so bad until 18-wheelers started passing us going down a curvy hill, pushing big washes of air that buffeted us with strong gusts of wind.

You don't notice you've been blown off-course until too late -when the lane lines suddenly angle beneath you.

Big, boxy, Class-A diesel motor homes aren't as slow climbing hills as RVs' reputation suggests. Speed drops to 50 miles an hour or so on the steepest hills.

Downhill is another matter. Then a big RV can wobble precariously, making prudence of paramount importance.

The engine brake - or "Jake brake" - is the first recourse to slow down. A switch on the dashboard programs the transmission to downshift radically every time you take your foot off the gas.

At first it felt like the single-pedal Disneyland cars that clamp on the brakes whenever you let up.

It also took some time to get used to other dashboard switches arrayed in neat rows, which controlled a confusing collection of dome lights, generator, taillight flashers, and windshield fans.

In town, the vehicle was little more maneuverable than a bus. I had to constantly check the outside mirrors to make sure I wasn't swinging the rear bedroom into traffic or fixed obstacles.

"Our" motor home had a full kitchen and bath, two beds, and two TVs. You'd think that would be big enough. But with our crowd, it definitely felt like camping - all the comforts of home, but none of the elbow room.

For us the greatest feature was the slide-out living room that produced 18 inches more walking space once we parked the rig. It also gave us room to unfold the sofa bed in the living room and a playpen on the floor for the one-year-old.

My wife and daughter and I squeezed into the queen-size bed in back.

The size of the group overwhelmed what little privacy the bathroom offered, though the plumbing kept up fine, at least when connected to the campground facilities. Otherwise, the water heater produced enough hot water for one shower at a time, but needed time to recover before another.

Unfortunately, the bathroom also housed most of the closet space and provided the only access to the rear bedroom. So privacy depended heavily on coordination, especially in the mornings as we all got ready to go out.

But alas, the legendary flexibility RVs are supposed to offer -pick up and go or settle down and stay anytime, anyplace - let us down.

The furnace blew out the second night with the temperature forecast to drop to 19 degrees. We got along fine with the help of friendly campground neighbors who lent electric heaters. But with no guarantee of where we'd stay another night or who the neighbors would be, we headed back to the warmth of Phoenix instead.

That's why this trip didn't quite live up to my first discovery of the Grand Canyon. The RV - rather than the canyon -ended up being the adventure.

Would I do it again? Sure. Even my 22-month-old daughter appreciated the awe-inspiring spectacle of the canyon.

As for me, a quick blast of the air horn -BOOOOOOMP - brought back all the boyhood dreams of why I wanted to drive such a rig in the first place. And the RV's failings suddenly seemed minor.

(c) Copyright 1999. The Christian Science Publishing Society