You are going to need to learn a LOT about electricity (far beyond the advice we can give you here) to trace each circuit and tag each wire as to what it works BEFORE you can even think about wiring it up.
Get a small motorcycle battery to test each DC circuit and just use a Home store to replace the 120 volt GFCI and downstream regular outlets.
An extension cord from the house plugged into a 15 amp breaker protected surge strip for 120 VAC power.
You will also need to drop panels and belly covering to make sure there is no damage to the wires.
This is not a project for the faint of heart.
If it is beyond your scope (and it may be), you need to hire a competent RV tech to help you.
If the camper is "road-able" (the running lights work), you should consider taking it back to the factory and pay them to redo the camper.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW