Rich,
YES to a roof vent, we leave one open just about 1/2 inch when we are fall and winter (cold weather) camping! It really does help.
Al and I have had any number of situations arise during our years as camper/RV owners, have to say (do you see me knocking on my wooden noggin???
) that we have not had trouble with mold.
Had mice; had broken frame welds; had camber go south on 2 trailers (one was a boat trailer); had axle trouble; had the brake wires break and loss of brakes more times than we want to remember or count; had the siding blow off the front of the last TT when we were hauling; had the front windshield cover thingy blow off a unit while we were hauling; had a few flat tires, luckily NEVER when hauling; been stuck in our own yard, van and trailer all hooked up and ready to roll, that was a fun day ! NOT!
But, please spare me from mold!
(Now you know why our phrase, Handy with your hands or handy with your money! HA HA)