Tom&Shelly wrote:A)...I don't know how well computer fans would work instead. If I were to do it, I think I'd put them up on the walls near the ceiling to expel warm moist air. I'd then have windows or passive vents down low to bring in outside air.
B) By putting them on the walls, it eliminates the problem of the roof leaking, although we haven't had that problem with our Maxxfan (with shroud). We have, often, had a problem with rain blowing in our side windows, so that might be a problem with the computer fans. Perhaps they would need some sort of shroud like a dryer vent?
C) Incidentally, back in the 40's, some of the teardrops seemed to have had vents up on the walls immediately below the roof, probably the thinking was also to expel moist air without roof leakage. I'd sure want to be able to shut them off for travel to keep dust out. Probably you'll want the same with computer fans....
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A) I have two computer case fans mounted on the walls, just below roof level. I can use them to expel warm air, or by reversing them, bring in cooler fresh air (thru insect screens). There are also two awning-style windows, mounted lower, that (also screened) bring in more fresh air (in milder weather).
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B) The exterior housings for the vents are waterproof (they were meant for roof-mounting, so mounted on the sidewalls, are doubly waterproof). I already have a dozen holes thu my roof (though sealed with PL adhesive and coated-over with a flexible membrane), so I never considered a roof vent (well maybe a Flexner, for a moment), and found a waterproof vent instead. And the awning-style windows really perform well, keeping out the rain, unless coming in a sideways gale!
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C) The fans are mounted on swing-outs (and can be turned towards the interior, if only a small bit of airflow is desired, or the main air circulator fan or A/C are not in use), behind a butterfly closure, that seal out dust & airflow, if not needed. I leave them open a bit, whenever I'm in the cabin, to expel moisture & carbon monoxide, no matter the weather conditions. The fans run on 12vdc battery, and consume so little current that I usually always leave them on, even when not inside.

- airflow & case fan detail.jpg (207.67 KiB) Viewed 1034 times

- computer case fan over vents for good, cheap air circulation.jpg (261.75 KiB) Viewed 1034 times