Good for you, rescuing an old vintage trailer. It is just the right size, easy to tow and fairly light weight. I have one exactly the same size, however mine is a Kenskill, Standy. I suggest you remove the old roof vent, clear off all of the old caulking and re-install it, after cleaning out the cobwebs and oiling the moving parts. Usually where these old trailers leak is where the roof meets the side walls, usually covered with a bendable aluminum moulding. At the very least, wire brushing the top of the mounding and caulking it with a quality caulking compound, would be a measure you can take to reduce any further leak problems. A more permanent solution would be to remove the molding, re-caulk and install new, larger screws, (the original screws rust and often allow moisture to enter).
Good luck, and with that price, you can't go wrong. Oh, yes, welcome to the forum. Progress pics expected!!

Roly, Vintage TTT and TD nut.