I have had many fiberglass trailers and now have a Scamp
and I have found the computer fans very helpful if you don't like to cut holes in the sides. I have mounted them in the roof vent and also in side windows
. The thing that really makes them work is to also make something that will block the entire opening around the fan. I usually make that out of a thin veneer plywood or corrugated cardboard that has been varnished for strength. The last one I made used about a 4 or 5 inch fan mounted to an approx 1/8 inch piece of oak plywood.. I cut the plywood just the size of the open halp of my kitchen side window and then cut a hole in it the same size as the fan blades diameter. then I riveted (you should all know about rivets by now) the fan to the plywood. Then I took out the window screws on that side of the window and put them back with those little flexible wire holders (plastic) that hold wires against the wall that you can buy at the hardware store. They stick out on the window side so I can slide the plywood under them to hold it over the open window area. I usually mount the fan so it pushes the air out the window- then I open another window in the trailer. It really is quite effective. The fans are easy to find at a swap meet, garage sale etc. and they come in AC or DC so you have a choice. I also use the small fans like this (about 2 inch size) for a fan in the refrigerator
outside area. Mount it above the heating unit and have it blow the air up. It helps make the refrigerator
work better on hot days by moving the hot air out. They are much more powerful than the commercial ones you can buy at the RV stores and usually cost about one or two dollars used.