The ground or negative terminal goes to the FRAME. It is usually black but in my camper it was white.
Find the cable that is bolted to the frame. Follow it to the battery and put it on the negative terminal of the battery.
What is left over goes to the positive terminal. May be red, but not necessarily.
The frame wire is ALWAYS negative or ground.
You should never tow the camper without a fully charged battery connected. If the trailer becomes disconnected, the emergency breakaway will NOT work and your camper will be an unmanned missile on the highway.
Lou, Laura, & Freya the wonder dog
2008 GMC Sierra 3000HD Crewcab SB Allison Duramax
2019 Flagstaff 8529FLS - Pullrite 3300
HAM CALLSIGN - KC3FFW