I wouldn't worry about tank expansion from the fuel. It's a concern for those metal tanks which are sealed and not vented. More of a concern are the charcoal canisters on new bikes. They should be removed and allow the tanks to vent. Yea I know that that is not the environmental thing to do but wait until your gas supply is ruined by the charcoal. We (BMW) riders have been removing them for years because they have been destroying our fuel systems by returning to the fuel tank by being siphoned back into the tank and vented into the throttle body dumping charcoal fuel into the engine. You will avoid all of the issues if you remove the canister (that ugly looking black plastic rectangular container hanging off the side of the engine). This will also allow the fuel tank to breath which is your original concern.