I prosealed mine in about three months ago.
A glob of proseal about the size of a golf ball will do both access covers as well as both of the fuel sending units and put some on the threads of all of the screws. You should even have enough to dab around on the exposed screws, etc when you are done, if you want to.
I mixed up smaller amounts, enough to do one side at a time, but if you have everything ready you could do all of them with the same batch. You do not need to put a lot on these surfaces, since it squeezes out and just forms a bead around the edges, both inside and outside of the tank.
39 hours and no leaks.