There are some products like that you can use, but they usually require another topcoat before you can apply paint.

If you aren't going to paint it right away, ask someone at an auto paint store to recommend something you can put on there.

Some catalyzed primers will work. There is also a sealer that can be used.

I would also recommend deciding what brand of paint you are ultimately going to use. The store can also recommend a primer/sealer that is compatible with the paint. Generally speaking, it is better to stick with one brand of products so each of them will work with each other.

Hey Guys,
I am in need of some painting advice.
I am repainting my 1200 Coupe. I have chosen my colour Mazda Phantom Blue. Before winter I stripped the roof and primered the it. I quickly found out that primer is not waterproof.

I was thinking of priming it with something like chassis black. Was wondering if I could topcoat it with acrylic.

Someone has painted it with some house paint so It looks like crap. Also I have replaced a few panels with ones from my other coupe. So I got a multi-coloured car.