Hi folks, I'm Mike. I have a 1993 Granby on its second truck, this one a 2500HD Duramax with air bags. Include the bags and an onboard compressor for them in your calculations.
After 22 years and over three years of nights in all kinds of places in this camper, I've replaced the following:
The fabric liner three times.
The roof covering once.
Roof rafters fixed where welds broke in the front from carrying a canoe on some right nasty roads. They also welded in reinforcements on those rafters.
The refrig three times - gas/110/12 three way. A necessity, but a pain.
The furnace once with a much higher output furnace with the same battery draw.
The water pump.
The foam and upholstery.
The door after the wood rotted. The new door was quite sloppy and took clamps and spreaders to install properly.
The roof vent once but I rebuilt the first one early on and it lasted for a long time.
The front turnbuckle eyes were pulling through the plywood. I premptively replaced the with steel plates holding a new eye bolt firmly.
The radio twice.
All the interior lights twice; once with fluorescents, now with LEDs.
Two gas bottles (style no longer allowed).
Umpteen deep cycle batteries.
Using this camper for real backcountry stuff beats it up and eats batteries and applicances with bouncing and jouncing. It's a small space and feet, shoes, and stuff dings and dents cabinets and doors. Leaks and condensation lift the vinyl from the siding panels. The washboarded north road from Death Valley washboards screws right out of the cabinets. Even the awning fails in the high altitude sun. We've not replaced it because we didn't use it much anyway.
If you use this like it was originally intended, you can expect to begin to replace stuff at, maybe, the 5 - 7 year mark, batteries even sooner. It's inevitable. But, this camper is quality built and is actually worth maintaining for decades of use - not like it's stickbuilt brethern.
If anyone is interested, I'd be happy to write up some other four wheel camper wisdom I've picked up in all these years of skiing, paddling, hiking, and biking from my Granby.