I just did this last weekend to my camper. Vent began leaking last time we were out so I knew I had to do something with it. Figured if I had to pull the vent to re-seal it, may as well upgrade. I had a vent, no fan, but I knew that 12v wiring passed around the vent to go between two lights. I bought a Fan-tastic Vent model 7350, a roll of buytl tape and a tube of dicor lap sealant from amazon.
The hardest part/most time consuming is removing the old butyl tape from the roof, especially if you have a rubber roof. Be patient, it'll be worth it. I happened to have a nylon trim pry bar set lying around and that was instrumental to the butyl removal.
Nylon Pry Bar Installer Kit 4 Pc
Sturdy enough to remove the putty but not sharp enough to cut the roof. I put a 4' x 4' sheet of plywood on the roof to spread my body weight around (i'm not light by any means), and went to work. Once you get the putty off, use mineral spirits to clean the remaining putty residue. Dry fit the vent, connect it temporarily and verify functionality, then put new butyl tape and screwed the vent to the roof and put the dicor around the flange covering each screw. After that, depending on your roof thickness, you may need to cut down the trim piece for the inside.
There's multiple videos on youtube also on how to do it. Not hard, but can be time consuming to get the butyl tape off, but well worth it.