The exhaust fan in the M109/M185 shop vans vents out the side and has a flap that opens when it is on, and has a cover over the outlet on the outside, and moves a lot of air. I bet you could fine one of those in a MV scrap yard.
We have one of those that I pulled out of the She Beast, in it's place I put in a 12v case fan to use as an stove exhaust vent. (the box is 12v w/ it's own batts & alt, and at some point soon solar panels) I'm planing to go the same route w/ this build as they are quieter and take up less space.
Of all the vents that I've dealt w/ over the years of rig builds I really like the ones that they use on the shelters.
I want to keep the mil style on the outside. If I can find ones big enough I may put some on the sides instead of windows . . . maybe I'll put in opening windows w/ covers made like the vent covers
. . . , . . . I still want a couple/ few vents for the front. W/ just the front vents open, the upper section of the door open, and insulation, I'll be able to take shelter inside during the mid-day desert burn and be ok. If I add some shade over the trailer (camo netting, shade cloth, etc.) and open the doors all the way, I'll be COOLLY spending that time relaxing
Oh, and MV scrap yards are far from us out here . . . unless I come across some in a ghost/ mining town . . . seen em