I went with this one. Like you mentioned, it allows the vent to open more than some other covers but I don't know how much difference that really makes. I have always had the vent open an inch or so while parked at home since installing the cover (for ventilation) and seen some heavy rain here. Not a drop inside the camper as far as I can tell.
Note that the instructions talk about removing four screws to install the vent cover, but Scamp
uses rivets, therefore I had to drill the four out and leave the rivet inside under the rat fur. Then, rivet the four brackets for the vent cover in place with plenty of lapseal. Not sure what the proper size rivet is to use here.
By the way, remove four clips (no tools needed) and the cover comes off for cleaning or whatever. Some people mentioned there is no bug screen but it does not seal so tight that a bug screen would make that much difference. I only have seen a few stink bugs come in and the fan chopped them up and spit them out.