Being 1000+ miles away, all I can do is research and connect where I can... Well, I can at least help with the backup camera deal... Video cameras generally have one of two types of connectors, BNC, and composite (RCA-style phono-shaped plug). The good news is, BNC can be adapted readily to composite. I'm pretty sure composite can be adapted easily to BNC as well...
RCA-style video cables MUST be MADE for video, a standard audio-style RCA cable may or may not work, I think I had some hit-and-miss trying this when I used my old B700 for a security shack... But if the connection is already a composite RCA, or can be adapted to one, a simple extension (male-to-female) RCA video cable (or two) should do the trick... Your power leads, quite honestly, can be simply spliced into your reverse light wires anywhere at the rear, inline with the sockets (there will be two wires, usually the lighter color is the 12V, the darker color will be the ground).
Were you able to connect with the guy that owns and built Transcendence? I understand he's pretty good with helping people with skoolie builds and such. Though I'm sure he would need a little something for the effort... Not sure what your financial / employment situation is...
Former owner - 1989 Ford B700 64-pass Blue Bird
(Rest In Peace, Cheese Wagon)