Pump it out and see what the fuel looks like. The pump will probably fail the first time you use it if it sat with ethanol fuel in it. If you see brown rusty watery liquid then you want to drop the tank. Does the fuel station even work? If it had the 10% ethanol blended gas it may be a mess in there.
I don't think my fuel station has ever been used, but my generator uses the tank too. I ride street bikes so gas stations fill those. Those plastic pump guts have to be ethanol resistant. The biggest issue is having water in the fuel, that will rust out metal tanks. Some trailers do have plastic fuel tanks, I owned a KZ with one. But, my current trailer has a metal tank and I'm thinking about dropping it soon. I'm smelling gas fumes too much when its full.