Yeah i have seen ones that slant like that. you could have it inside the roll bar and attach with velcro loops, i had a tent sort of like that once.
I think i would also like to have at least one side be able to open out into an awning, but then again these truck are so small that even a roof rack mounted awning would be about neck level for me. My tray fits a double matress perfectly width ways on top of the wheel wells, and has about 20cm extra length, so I might throw in a ply false floor and store some camp gear underneath for ease of construction and use.
I hope to park up next to some fully decked out 4x4 'expedition' trucks and show them how fun a small, light, minimal truck is