We have a 2006 T139, so may not be the same, but ours had a non operable skylight that had cracks in it. we took the skylight off, and put a fantastic fan in. it was hard to pry off the skylight, but super easy once that was done. our camper even had wiring right to the hole where the skylight was. My husband used dicor non sag lap sealant to adhere it to the roof, and seal around the edge. (I think he should have used butyl tape, but he was the one on the ladder...) one thing, you really should either put a fresh air intake in the bathroom door, or plan to leave the door open while the fan is running. it pulls a lot of air!
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