Unless you want a project for a few years, and don't care about camping, run away from it. You will probably spend about $8,000 to $10,000 on a major renovation, parts alone. All you are really starting with is a shell, and that is not worth much. I spent about $6500 on my '74 Argosy 20' four years ago, and it was in pretty decent shape to begin with. No floor issues either.
Any 40 year old original trailer needs mostly everything from axels to all appliances to door locks, to furniture and you already mentioned the window an floor situation.
Spend your money on something that someone else has done the work on, and go camping.