My new NH1630 was outside for the first two years, now it is inside with the motorhome in a new garage built by a local contractor selling Americbuilt buildings, a company from MN.
It is a well built building and a lot cheaper than a Morton.
After two years outside, there was a small amount of fading on the hydro control lever covers. Other than the one item, it was fine. The storage keeps the sun off, which seems to be the biggest problem with outside storage.
Contrary to some of the things that I have read in these forums, rain does not hurt the tractor. provided that they are kept fairly clean and washed once in a while, so that a place for corrossion is kept to a minimum.
If you look at any of the old farm tractors, what do you see?
Fading of the paint, caused by the sun.
Keep them in the barn, shed or build a sunshade of some sort and it will keep them looking a lot newer, the rubber parts will last a lot longer and so will the seats.