Here are a couple of bits of preventative maintenance that will save a soggy interior and seized filler cap hinge.
The MkIII Roadster is prone to waterlogged interiors due to the clogging up of the two drain valves located behind the side engine vents.
You can check if these are clear by pulling the hood about half way back and looking down between the hood and body side near the engine intakes, if it looks dry then all is well but if you see a pool of water then likely as not the drain valves are blocked.
The side vent covers are easily removed with a little care and clearing the blockage is very easy.
While the nearside cover is off it is possible to access the filler cap hinge behind, this can then be lubricated which will prevent the inconvenience of not being able to fill up.
Here are the photographs I took while doing my car.