strong gas smell is a leak...either fumes...but in most cases its a gas leak...if it has a very small leak under the tank it will smell bad in the rig....if it has a bad fuel line hose coming off the tank...it will smell bad...if the sender unit is not sealed and losse it will smell bad...
in 18? years its only smell'd bad 3 times...its a good way to find out you have a problem before the problem gets out of hand...your gas leak sensor in front of your face is a very helpful tool
check lines ......check sender....take out and check the actual tank...and as others said check the vents...not nesesarily in the order