
What about getting on of those green/cream plastic boxers from one of the DIY stores.
We have a Caravan in Wales, an lots of people (me included) have them, many store washing machines and freezers in theirs , plumed in of cause.
I have had mne for a few yrs, now, they dont let any water in, and aesthetically look much nicer than a tarpaulin thrown over them
http://www.jellydeal.co.uk/plastic-sheds-and-storage.html