Just for the record, Fan-tastic does indeed make models that do reverse, and can be used as a low volume downward fan. I have two such fans in my 2004 Designer. The model is 2000TRS, which has wall thermostat, rain sensor, automatic or manual opening dome, and reverse switch. You simply manually close the dome (or leave it slightly open) and set the switch to downward flow of air. Have used it many times this way, with no problems. Automatic feature works great if you want to leave for a while and not get rain in your rig.
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.