COMPLETE rewiring

See if you can find somebody to give you schematics for a similar rigs and use them as a guide.There are some soft cover generic RV maintenance books that may have helpful schematics and block diagrams. Selecting the proper guages of wire, connectors, splices, heat shrink tubing and 12 volt DC and 120volt AC power panels, hardware and electro-mechanical devices will be a large part of the process. Securing wire/cables and protecting wire from abrasion and shorts and connections from corrosion, are important. Getting advice from others that have refurbished and modernized old rigs should help. It may be possible to locate OEM schematics especially if your "toy's manufacturer is still in business. Did you take pictures and make notes while tearing the rig apart?

PS: Wherever practical, soldering is preferable to crimp-type connections which may come apart or corrode causing poor connection problems over time.