I'm guessing the bed will steel be steel, or at least have steel inserts on the inner walls and load floor.
I don't really see any issue with an aluminum body or chassis as long as it's designed and built correctly. Peterbilt has done/does it.
1987 Ford Ranger XLT 4x4 2.9
Needs a lot of work, including some rot on the body, but shes getting there.