Peeling and bubbling paint is poor adhesion, caused by low quality paint, bad surface prep, or a combination of both.

Especially in an outdoor coastal environment, the highest quality paint is necessary. I like Benjamin Moore, but Sher Williams is also good. Spend the money for the best stuff.

Surface preparation is critical no matter what environment you're in. You are going to have to scrape all of that bubbling paint off. You should be able to see then if the top coat(s) is not adhering to the primer, or the primer did not adhere to the substrate. Dirt, moisture, or other films at the time of the painting will interfere with the bonding. Too smooth of a surface may also prevent good bonding. Paint is a mechanical bond, the rougher the surface, the more surface area there is, the better the bond.

Since it is a flat surface, I would take a disc sander to it. Get some 80 or 100 grit and get busy. Wear a mask if you do not have a vac on the sander. Wear gloves for hand sanding, sanding creates heat and after awhile, your hands/skin will feel it. Hand sand the thinner areas and edges, disc sanding the big flats. Try to do it on a dry day (I know, coastal area, dry day?), if you sand in a very humid environment, your sand paper may clog up quickly. Don't be afraid to round over the long edges with hand sanding. When paint dries, it contracts a bit, really sharp edges end up with the paint pulling away slightly from the edge as it dries, leaving a very thin or not coverage.

Clean trim with a rag and/or a vacuum. Any voids, fill with Bondo or caulk. Any areas where you are down to bare wood/substrate, you need to prime. Then top coat with at least one coat. Two is better.

There are few other tasks on a house which are more fun than this. <sarcasm> Good luck.