The M1010 is 10,000 lbs GVW, 19' long. For $35K, you could buy a truck, replace the stock drive train with a turbo 6.5 diesel, 700R4 transmission, and either a GearVendor overdrive or a lift with bigger tires. (Bigger tires improve your off-road performance, but you have to be strong enough to fix/change the tires on the trail. Bigger tires get *heavy*.) That would leave you ample budget for any needed body work and a nice paint job, convert to all LED lights, mount a winch, add a house bank of batteries, replace the entire brake system and upgrade to disk brakes, add cab A/C, add tunes, add additional fuel tank(s), tow bar, arctic heat, plus upgrading the electrical system to eliminate the DUVAC. You'll also want a video system to show you your *huge* blind spots, a tall cell-phone antenna and booster amp, and a fairing on the cab roof (helps mileage a lot at highway speeds). I added an M1101, which exceeds your 25' length, but you have the option of 19' without the trailer for exploring the tighter trails.
This would give you a 19' 5/4 ton chevy that cruises comfortably at 75mph, sleeps 4 comfortably (5 in a pinch), and seats 11. (One seat is weird, more like a harley saddle than a car seat, so maybe call it 10.) Fuel fired heaters run off a house bank would keep the cab and box warm, and would warm the coolant and batteries if it's cold enough out to warrant that. The footprint is a little smaller than an extended cab chevy pickup, so you can park it in normal parking spaces. The tall antenna would give you comms in the fringe areas.
My rig retains the stock drive train, brakes, paint, interior, tank, and most lights. I haven't added the cab A/C, fairing, comms or tunes. It's a work in progress. Including the trailer, I'm looking at about $12K invested. This is with very rudimentary sanitary and cooking facilities. Mine is a camper, a substantial upgrade from sleeping in a tent, but not a living room on wheels like a larger motor home. It's also massively simpler to operate and maintain.
For my rig, I left the original M1010 intact. I can remove the cooking/sanitation/refrigeration gear and the truck would be at home in an MVPA event. (As long as no one opens the hood and inspects the electrical system too closely. The trailer hitch receiver, winch hawse, and rear slave socket might offend a purist, but most folks wouldn't mind them.)
You mentioned that the $35K budget does not include the camper. If you already own a camper, you might consider a M1008. It's a 5/4 ton CUCV like the M1010, but it's a pickup truck that would handle a camper well. The M1010 has an ambulance box on the back rather than a pickup bed. For my purposes, the M1010 works better than a slide-in camper. YMMV.
The M1010 exceeds your 4-ton max weight by a ton, but includes the "camper". The M1008 would not. The other MVs are *much* heavier than your max limit.
