Re: 1997 Dodge 5.2 poptop value
Basically your value is in the van body and the PH, so I'd look at the book value for the van, add in a percentage of what the PH would cost to add, and have that be your number. Your van itself looks very nice. Unfortunately it seems that Dodge vans usually go for less than the comparable Ford SMBs, just because the platform is not as common and doesn't have as many aftermarket accessories, etc., available for it.
The average home build interior only adds significant value if it's really well done and basically in line with what a stock SMB (or other RV) interior would be like. In some cases, it might actually diminish the value of the van. Yours looks functional but not much more than that (at least from the photos), and unless you get the exact perfect buyer, they will likely be thinking about tearing it out or significantly redoing it IMO.
I would clean up the interior a good bit, perhaps enclose those wires and the area where the PortaPotty is, restain/varnish your sink countertop, etc.