I agree with Paul, and this has been covered here in the forums many times.
These threads commonly pop up a number of people that have used the cork or rubber gaskets and mention that they have had no problems, but they usually have relatively new, low time RV's.
The reality is the gaskets can work, but are pretty much guaranteed to leak eventually. Use of proseal (if done correctly) is pretty much guaranteed to not leak... ever.
So you can choose ease of removal over a high likelihood of them needing to be removed at some point in the future.
Also mentioned in previous discussions....
The way to make the sender or cover much easier to remove when installed using standard B2 or B1/2 tank sealant, is to not fully tighten the screws. I.E. leave a thin (.020-.025") layer between the parts to allow for a putty knife to be tapped through if you ever need to.
The down side to this is it increases the probability of a poor ground continuity between the tank, cover plate, and/or sender flange which will cause a the fuel gauge to not function.
The way to overcome this is to put an internal or external tooth lock washer under at least one screw that mounts the sender, and one on the cover. This will assure electrical continuity between the screw head and the plate / or flange, even if the plate is not tightened down fully.
The washers are specified in the build drawings for the new kits, but it would be beneficial on any RV model.