Got a great idea from someone somewhere... would give credit if I could remember who. 

Some sailboats have waterproof solar-powered vent fans in the deck to keep the cabin aired out.  I think I'm going to put one on my wish list for my non-LQ trailer... I have no power into the DR.  This one, which has an on/off switch (they don't all have one), is only $200.
http://www.discountmarinesupplies.com/Solar_Vents-NICRO_POWERVENT_3000_WHITE_ABS_VENT.html

Check out Ebay. I saw some less expensive ones when I was recently surfing. Marine grade items are quite pricey. Compare CFM ratings to get comparable performances and costs.

BOL  Gard