Regular Conversion vans are designed as people/family movers, not camper vans
There will not be any extra battery, 110 vac receptacles unless the previous owners has added some.
There will be some extra wiring for lighting and the TV's.
Older gel coats on weathered fiberglass might not be the best place to test VHB tape. There are usually some wood runners sandwiched into the fiberglass top which can take a screw OK. Mechanical fastening a solar panel will likely require removing the ceiling interior panels.
The 5.9 dodge might eeek out 16mpg highway at 65mph.