I have a 2011 Nissan Sentra thats smells like gas once in awhile.

Eddie Carrara

The car is a security vehicle it smelled like gas one day after driving all day in the heat about 2-3 weeks ago but I couldn't find any leaks.It happened again yesterday so I checked the gas tank (Without dropping it down)the fuel lines,fuel injectors and gas cap but I couldn't see any visible leaks the mechanic i go to said it could either be the fuel pump where it meets the tank or the canister but usually those problems would cause it to smell more frequently could there be any other cause?