Phil,
You mentioned you were getting prebuilt tanks, so disregard the quart size as mentioned above. A 1 ounce container will cover one trailing edge (though the left elevator has a small trailing edge due to the trim tab, thus 2 containers will do both elevators and the rudder). The 1 ounce and 3.5 are fast setting, so quick work is needed if you do all three at once. Another option is T-88 epoxy - at least this stuff can be used for many purposes in the future, whereas the proseal is a one shot deal. My plan was to do the elevators and trim tab foam ribs at once, so I used the 3.5 oz. cartridge. I do have Van's gun, also, so it was easy to apply. If you do the cartridge (one will do all three surfaces with plenty left over), you can use a regular caulk gun, but may have to grind down the plunger disc to fit inside the cartridge tube. After mixing is not the time to find out! If I was to do it over, I would get the T-88 due to high cost of fuel tank sealant and high shipping and handling at Van's. Plus it is about the stickiest snottiest **** I have messed with.