Thanks for all the helpful info.
I think I will try building a small room within the shed,with unsulation, and a small AC unit in it.(if nothing else,I will put the other computer in there !!)
I have watched the humidity over the last week and it changed from about 45 - 65 % and about 21 deg C
I have a lot of timber stored in the shed (Cedar,Rock Maple,Ash,Pine etc) and none of it really seems to move.I know its a lot thicker than the sides/back and top but if any thing this would be a good indication - I hope.
Thanks
Greg