[rotorwrench]

Some car covers are just to keep dust off in a garage storage. Water resistant multi layer covers are as good as it gets but are expensive.

Shaded areas are good unless it's an area where rain water can come off a roof. Avoid any area that multiplies water exposure during rain storms. Trees can also shed leaves and branches during storms so I'd avoid proximity to them as well.

Tops should be stored in the upright position. Folding the material puts strains in the creases so it doesn't help to do that. Most model T windscreens are not foldable but they can be removed.

I would suggest leasing a covered storage that allows automobiles. Some mini storage places will allow car as long as the fuel is removed but that would likely require light oil in the tank as a preservative. The place should be insulated if it is enclosed. They don't like anything that can cause or propagate a fire.