I would confirm you have a big enough power supply first? Add up the number of bulbs you expect to be running at any given moment and see how the total amperage draw compares to the amperage available? For instance, if you are trying to run 4-6 lights off a 4 amp battery charger, you can plan on having some pretty dim lights when all are on?
If that's OK, then I would assure myself there were no more than 2-3 lights running on a set of wires.
I remember some of these oldies not even having 12v ceiling lights. They used 1 or 2 propane lamps...
1997 37' HR Endeavor, 275hp Cat, Freightliner
03 CR-V Blue Ox, Ready Brake