I can see why you'd find sleeping in the truck uncomfortable. I'm 6' as well, and I tried building a platform in my old Disco. Worked fairly well, but you couldn't sit up, even with the tall profile of the Land Rover. Made getting in and out awkward, and it felt too much like a coffin for my liking. The only vehicle I could see doing a setup like that in is a 70 Series LC Troopy. Those are massive inside.
And it's colder than most people would think. Sure, it keeps the heat in better than a tent, but once that's gone in an hour, it does a great job at keeping the cold in too. Unless you want to get up every hour to get the heat blowing. No thanks.