Food for thought…Id want a slightly weaker tank in the event of a crash. If the epoxy is too rigid, you have a shrapnel machine that is spilling fuel all over the place.
A fuel tank shouldnt be like say a bracket that supports a load. It should have some give before it blows apart.
Id love to see how you go about making this tank. Maybe a pic section on how you molded it and built the composite tank?
oh and on the vent idea…the vent should only allow air in not anything out. They usually have a one way valve on them. You vent to keep the tank from having vacuum build up in it. In heat without a valve your fuel would start spitting out all over the place and create a potential hazardous situation for fire!