Sounds like you have a short somewhere. Start in the trunk and check the exposed wires if any are accessible. The GFCI plugs are for 110v and the fuses are for 12 volt. The red light in the fuse panel comes on when a fuse blows. Hopefully someone with a camper like yours will jump in. Also in addition to the year and brand please include the model . You can add it to your signature then others will know what camper you have and provide better help. The problem with a short is that it could be anywhere and anything from a bad furnace to a bad light to a wire touching a source of ground.
When they wire the campers several things are on the same run or line. Like your furnace and stereo. also you can disconnect - one at a time- each thing that does not work then try the fuse to see if it still blows.
2005 Cruiser 29CK
2008 GMC 2500hd 4x4
Crew cab Long bed 6.0 gas
4.10 gear ratio