Is it better to use oil based primer under latex paint? Will it hold up better? This will be used on new wood. Thanks

We have a wooden door over our crawl access. The paint keeps washing away from rain dripping off the awning overhead. Can it be sprayed with a Vinyl Spray Paint? Where can one buy this product? Any other suggestions?

When preparing metal flashing I was told by an ex painter not to scrape or sand these parts as it will take galvanizing off and rust,is this true?

Can I paint over two coats of exterior latex primer that been dry for a few days? I read somewhere that I need to add another coat of primer if it is dry beyond a few days.

So, after working on my fiberglass door, the results are not ideal. What I would like to know is if I can get a different gel stain (one that would help to match the door with the wood surrounding it) and stain over what is already done? Any one out