Thoroughly getting rid of the rust is the key. Then prime and topcoat.
I have used Corroseal before. I am not a fan of it. I have found that the amount of time I have spent doing the recommended corroseal prep work, again and again, and again, would have been better spent doing a more thorough job of prep work, and just doing it once.
A properly prepared surface will last two years ( yeah I know how much work it entails!). So why use corroseal to have it last two years? Do it right and just keep up with the spots.
I do use OSPHO. Mixed results, but it is cheap and easy to use. BUT, you have to chip/wire wheel first. You are using needle guns and wire wheels right? Not just chipping hammers, peening over the rust, making nice small holes to start percolating rust bubbles from?
Have you had the deck / house professionally sandblasted recently? Ever? Although this is just my opinion here, I feel that the companies that are too cheap to do the occasional (3 to 5 years) total surface prep in shipyard are penny foolish, steel pound replacing over time. BUT, trying to beg the management to spend the $$ is tough. "Aw, just let the crew do it, it's cheaper" Yeah, but then you need to crop and replace........