Marine-Tex Gluvit™ waterproof epoxy sealer makes an ideal barrier coat to protect aluminum boats from water damage, abrasion, and galvanic corrosion. You can use it on leaky seams and rivets, or coat the entire hull.
The amount of Gluvit you need to seal a 14 ft. aluminum boat depends on freeboard, hull shape, etc.
For example, let's say the boat is 14' long, 16" freeboard, and 6' wide. Conservatively, 14 x 6 x .85 (the bottom profile is calculated like bottom paint) = 71.4 sq ft. Then conservatively, each side would be about 14' x 16" (yes, it flares and tapers—this is just a rough estimate) = 16.3 sq. ft. per side x 2 = 32.66 sq. ft. plus the transom of 6' x 16" = 7 sq. ft.