[AZKen]

I agree with ED. None of those owner add-on's are "options". They are not necessarily favorable or valuable. Most of us would weld up the holes.
You don't say what is on the other side of the cab connector. Could be wires going to engine bay. Look for evidence of two 12V batteries.
If it was a communication link...it's a guy wanting to talk to his wife while she was resting in the camper while he was driving....or
vice versa. 12V wires for camper power will look different than com wires.

The tanks could have been for a rancher, farmer or maintenance truck full of diesel or ? If tanks were for the truck, look for a valve under/next to seat and some abandon fuel lines inside frame rails.

A camper AND bed tanks would be a little "different". Maybe tanks were under bed?

Does seem to have camper rubber rub/witness marks.