Sparky's got a good point- although by plugging it, it would be safe to move to a generator (no chance to feedback)
If you're going to go that route, don't cheap out on the connectors.. go with watertight marine, like is used for ship-to-shore...
http://www.lockingpowercords.com/pro...ceptacles.aspx
http://www.lockingpowercords.com/pro...ght-cords.aspx
(have never used this website before, but am familiar with Hubbell power cords)
seems like overkill, but having it sealed will reduce corrosion over time (since the shed won't have air conditioning, right ?)