Stripped Webasto wiring...

[windy]

Yeah, been reading up on the FSR, though the car's not really showing any signs of the AC/blower playing up.

I think the Webasto has run-on once or twice after I've turned the engine off, but only for maybe a minute or 2.

What happens if I remove/unplug the FSR till I get a new one?

[amacman]

if it`s not a parasitic draw it will be because you are not running the engine long enough to charge the battery , just as you said .
you could try using a solar charger . these are available from Maplins for reasonable cost .