The roof vent over the bunk of my trailer is the escape hatch.  The previous owner installed it.  It's a larger than normal size, about as big as 2 normal roof vents.  I really want a 12 volt fan in the vent to suck hot air out during those summer nights when I don't have air conditioning.  Has anyone found a pre-made vent/fan unit that isn't standard size?  I find it hard to believe that there was no fan in the vent from the factory, so I bet there's wiring to it that got covered over when they installed the escape hatch.   If not, there are enough 12v. wires from the bunk lights that I could tap into, so power isn't a problem, but I can't shrink the size of the hole in my roof.  Do fantastic fans only come in one size?

Amanda