You have been incorrectly advised. The Fantastic Vent (fan) fits nicely in the Burro
roof vent location. I installed a FV 4000R in my Burro 13 last month. It was relatively easy. The stock vent hole 14"x14" is the perfect size and it is located in a relatively flat area between the ridge spine and the roof side curvature. When you order it, tell them that you have a "thin roof" and they will cut the inside trim smaller (about 1 inch high). If the wires in this location are wimpy or non existent, it is easy to fish a wire into the vent area (between fg layers) from the cabinet over the sink, which has 12V wires in it to power the cabin lights
. Just follow the FV directions and go slowly.
The most difficult part is access since most work is from above and you cannot really sit on the roof (I cheated a bit). You should have an 8' stepladder, or better yet, construct a scaffolding that spans the roof and you have it easy.