Didn't have much luck with Gamma Seals
I too attempted a 5-gal bucket canister project. I had a real problem with leaking through lids. Basically, the incoming water pressure was too great and it became too tight of a balancing act to match output with the input.
As you may have guessed, the $3 lid from Lowes/HD leaked around the seal. I had even put airline tubing from the lid back up to the tank to help relieve inner air pressure. No go, I needed some sort of mechanical lock-down to help keep it sealed.
Enter Gamma-Seal Lid:
Originally thought to test it's sealing by filling the 5-gallon bucket with water, sealing it up with the Gamma Seal Lid and hold it up over my head for a bit. No leaks after 5 mins of jostling it trying to create inner turbulence. Set it on the ground upside down on the pavement for an hour; still no leaks.
But upon hooking up the of the incoming water lines and outgoing pump-line, once the bucket filled with water, it began leaking through the screw in cap of the Gamma Seal.
I gave up on my endeavor after the 350gph Cascade dropped down to $100. You may be able to apply additional sealer to the inside lip of the screw-in portion of the gamma seal, but I didn't get around to it.
Hope some of this info aids your cause.