Sounds like a nice project you have there.
Have you looked at Vintage Trailer supply . com?
Vulkem works about the best.
Is the leak from the antenna coming from the shaft thru the roof, may be an O-Ring that needs to be replaced. Not a fun task. May need to seal around the base of the antenna. Check this link out for a leak similar to yours
Can you post pics of your vents, sounds like you should look into replacing them.
Interior lights? Do you have 2 batteries? I have a switch that transfers the power from the RV battery to the ignition, not a good thing if you want to maintain a full charge. Do you have power to the DC lights when you are plugged into shore power?
Check out my restoration on my '77 20' Coach