The camper is in Georgia? Right now with all the rain and such?
I'd get a blue tap up on the area where you think it's leaking using gallon plastic jugs filled with water hold it in place along with any ropes and bungees you can scrounge up. Meanwhile, try electric heaters to evaporate the moisture, and perhaps rent a large dehumidifier. Than when it's better weather, expose that leak area to the hot sun you guys get in Georgia. Give the wet area several days to dry while blowing air on it with fans.
Once that's all done, then decide whether to remove a wall panel to look behind it or determine if it's dry enough without pulling a wallboard. Than put Eternabond 4" tape over that roof seam and never worry about it again.
Roof sealing...