However, if he’s tall and the truck isn’t too lifted, an assisted standing position is totally doable. The person being penetrated can rest most of their weight sideways in a seat, while the penetrator stands outside of the open door. Call it T-boning!
Bed of the truck? Sure, if you’re somewhere remote and you don’t mind bugs biting your ass. AND being on the bottom isn’t comfortable in the corrugated beds... unless you have a few hoodies or blankets to soften the surface beneath you.
Eyes on the road in compact cars
In a small car like my VW, I'll have my lucky passenger sit in that seat, and I will sit on their lap with them inside of me, both of us facing the same direction. He can assist me in my humping and grinding, and if trouble comes, I can quickly scramble back into my driver’s seat.