I wonder if a guy had them powder coated or even just painted ,
Would that
Help prevent the leakyness
That seems to eventually come about ?

They don't generally leak from porosity in the casting, but from corrosion buildup on the tire bead seating surface. I'm not sure if paint would help this. The powder coating I have seen has a slightly roughened surface; sealing surfaces must be as smooth as possible. Some of these wheels used to be chrome plated, but the plating itself would flake off and cause leaks.

If you are really worried about porosity, have the tires removed, get some epoxy paint and apply it onto the inside of the rim, the part you can't see when the tire is mounted.
Air pressure will push against it onto the surface. If you apply it to the outside, the air pressure would be lifting it off the metal of the wheel.
An easy thing to check is that the valve stem core is screwed tight into the valve stem.

once the corrosion starts you have to wire wheel the inside sealing surface to get rid of it. And if its bad coat it.

I once had a leaky aluminum rim. It was where the bead sits but it was leaking on the inside of the rim albeit VERY slowly. Rim got wire wheeled and then they putsome bead sealant around the rim. Didn’t have any problems for the 4-5 years I drove it after that.

Every cast aluminum rim I have examined up close has had a clear coat on it. It’s obviously to seal out corrosion but repeated tire changes is going to degrade it and allow aluminum to be exposed to air which starts the oxidation process. Forged aluminum is far less porous but more expensive to manufacture hence the common use of cast rims as factory offerings. Both cast and forged aluminum rims are more prone to scratches from steel tire changing parts which I suspect also contributes to leakiness.

G.M. Technical Service Bulletin 08-03-10-006G dated November 2019 gives the approved method for repairing bead leaks. I would imagine other automakers have issued similar TSB’s.

Keep this in mind when dealing with chain tire stores. Your results may vary but last winter a simple low tire condition on one was made out to be the need to replace all four wheels and a new set of tires (whole other story) that were still within tread life. Oh, and an offer to finance the whole package with instant approval. And when I brought up bead sealer, I was told “It’s a Band Aid, it doesn’t work!”

No I didn’t bite, unfortunately for him close to a half century working in car dealerships taught me a thing or two. We were using a form of bead sealers on the C3 Corvette YJ8 aluminum wheels in the late 70’s so that’s been around for a long time.