Running Inverter Generator Safely From Pickup

I run our Hondas regularly from the bed of my truck. I drop the tail gate start the generators,spin them so the exhaust faces out. The tonneau cover stays in place one fold open, depending on expected weather,if rain is expected I leave it flat. I have a trifold. I have set my extended run tank on top of the cover.
This is for overnites only so I normally do not unhook the trailer. Once set up in our spot the generators sit on a piece of plywood on the ground.