I'd suggest to pull it out onto a surface where it can be inspected. Jack up the suspension and pull the drums. Inspect and confirm that the brakes are working. Inspect hubs and bearings for adequate grease.
I've pulled trailers out of swamps where they were buried for many years. It is a roll of the dice what you'll find. My '71 Starcraft was driven 30 miles to my house on the tires that came with the trailer. The water damage was so bad that I could put my arm through a gap in the wall siding. It has, since, been restored.