Nothing yet as my tougne boxes (yep, two) are not built yet. Each will be only 18" wide with a propane tank nestled between them.
One will house my 12V battery with fuse block and ground buss for my 12V DC systems. The other will house my 30 amp main breaker box, my shore cable, my battery charger (connected to the battery via a PVC tube between the boxes) and if there is room, my water hose or stack jacks. I have my pickup truck to carry larger items such as popup tent canopy with screen, lawn chairs, grill, etc.