My friend built his own version on a 1088 Unimog U1300L chassis with an Alaskan topper. Global Expedition Vehicles
can build you a snazzy one but you'll drop $400K on one...
Or there's Marc's XP-Camper:
And Dale put a Flip-Pack on his Power Wagon:
And I had a South African trailer made by Conqueror before my teardrop:
Power Wagon: When only the fastest-depreciating, least reliable, fuel-thirstiest, oversized land yacht will do.