i personally cannot be bothered with this... i just leave my bike where i can, if that is in the rain, then so beit.

my bike is ten years old, is left out side, under an awning every night and there are no reall problems.

just keep checking the chain and cogs, keep them gunk free... i just de-gunked mine for the first time in 3 or 4 months because i kept forgetting to do it..

regarding the seat.. your pants are water proof, so what is the big deal? but those plastic shopping bags are used the world over, they will last months, if not years and the handles can be used to tie the bag round the seat post....

robi