Since we're talking about alternatives, I've found a fabulous way to keep the
Boler cool with just a fan. I copied the "blow the warm air out which will suck cool air in" method that I've had good success with in houses.
Those of your with a Fantastic Vent are probably enjoying this already, but for those who don't have one (or who are wanting to use a 12 volt fan)...
When I'm plugged into power I use a regular 20" box fan like you can get at any hardware store or Home Depot type place for under $20. You could also use something like a Fantastic Fan (12-volt box fan). The idea is that the fan fills up the window without side gaps.
So, I have a "counter" that runs across the foot of the dinette bed (from the sink counter to the rear wall - it's about 18" x 42"). I set the box fan up on that, facing to the outside, and let the pulled back curtains help to seal the sides. It already fits top-to-bottom just about perfectly (there is a slight gap at the sides due to the angled walls). I open that window all the way (I have jalousies), then turn the fan on.
Immediately, nice cool outside air begins to pour in the other
windows (the fewer other
windows you have open, the more of a "blast" you will get through the open one(s).
With this set up, I've been able to keep the camper within 1º of the outside air, even in direct sun, in hot muggy weather. Of course during the day, it's still 90º inside if it's 90º outside; but at night when it cools down, the camper is instantly as cool as it is outside. None of that nice cool outdoors, but then you come inside and "ugh... hot." Even in a really hot climate I find that it usually gets down into the 70s at night, and with a breeze that is pretty comfortable.
Sometimes I even have to close, or partially close, the window at the head of the bed because it gets
too cool (even in "hot" weather). By manipulating the window at the head of the bed I can adjust the breeze.
Raya