If you want to fly with mogas, don't use MGS-335 in your tanks. John Slade has proven that MGS-335 deteriorates over time (it takes years, but it does happen) when exposed to mogas, most likely due to the ethanol that is in it now. Various solutions have been proposed, including a range of tank sealants, the use of alternate epoxy systems like EZ-Poxy, and even building internal tank layers with vinyl-ester (which is designed specifically to resist chemicals, including alcohols). In my case I chose to seal my tanks with Pro-Seal. This process isn't hard, although it is expensive. At the time I wrote this, Aircraft Spruce was selling a quart kit for $150, and I ended up needing two.
The tanks were built per plans, but before attaching the top skin they were liberally coated with the Pro-Seal. This included the sump cover and the inside of the top skin, excluding the area around the T-hats. Pro-Seal is a manganese dioxide-cured polysulfide compound. Polysulfides (which, incidentally, my tank level sensors described below are also made of) are particularly resistant to chemical attack, and ethanol in particular. This solution is untested. However, I believe it to be the best choice for my aircraft. Pick a solution, but whatever you do, do something.