[EC900]

If you recently topped off your gas tank and or spilled any gas and it ran down to the overflow tube, you might experience some lingering odor.
Gas should not be entering the fuel vapor expansion line unless there was an overfilled tank and some really wild turns and curves.

“… Could this be related to the evaporation tank in the wheel well or its lines? I’m not too clear on exactly where those go…”

Not sure if ‘88 has exp rank in fender well like the 74-77s +…with the washer fluid tank and the fuel vapor expansion tank behind it - but if so, did you did all the replacing hose and expansion tank, (or someone else) then make sure lines are correct that fumes are being drawn by vacuum back to into engine and charcoal canister is connected. If I recall it’s not easy to mix up lines due size of hose stubs, as for vacuum…It’s a 4mm hose and gets very brittle back there in engine compartment, if broken then no vac and odors could be backing to a weak connection in the trunk.
Smoke test the expan. system is one method, low pressure 1 psi max. But if you don’t have a smoker, just use air and be quiet enough to hear any hissing.

There’s plenty of diagrams for the expansion vapor system showing the route and connections.

Also, cabin to engine compartment is not so air tight either, so check that odor isn’t from a fuel line hose back there just in case.