Assuming it's Gas-O-Line...
Many RV's have a "fuel filler" that connect (with flexible hose) to a large tube (fill) and a small tube (vent) that lead from the filler toward the Gasoline Tank. Then there may be a bend or two and finally connections to the Tank (more flexible hose).
The flexible tubing can break down and allow leaks of liquid gasoline and/or vapor.
Another possibility - There's an evaporative canister under the hood. Several small tubes connect to it. I've had them break down and allow lots of odor into the engine compartment, which isn't all that far from the cockpit.