Corrosion protection inside of wings/emph/fuselage, et.

I pretty much need you help here as I will begin construction on my RV-12 soon. I have decided 'definitely' that since I live very near the Pacific Ocean, I need to spray some sort of corrosion protecting 'primer/sealer' on the interior surfaces.

I purchased enough NAPA 7220 to do the job and thought that would be good. Upon the advice of several posters here and some more research, I now think that the 7220 might be good for the first coat but that a two part polyurethane might be much better.

I really don't want to do a two coat procedure if it isn't necessary.

And how about the Steward water born products - anyone used them on the 'inside' for corrosion protection? As a Cancer survivor, the Stewart products are appealing from a health prospective.

Right now, I am pretty well confused - can anyone who has experience with and of the primer/sealers please set me straight? Not concerned about 'primer was' - just need direction - please.

I used Cortec-373 on the interior in the wings, tail cone and empennage. This stuff is pretty tough to salt spray even without a top coat and without sun shining on it I didn't see the need for sealing it. It's not problematic to human beings or the environment and water soluable, dries quickly, easy to spray, one component, can be rolled or brushed on as well.
On the forward fuselage I am using Stewart primers now. Mainly because I want to paint the interior with their polyurethane and make sure there's no chemical incompatability with the Cortec-373. I am using both primers, the one component and the epoxy primer. The epoxy primer is very easy to use, gives a wonderful finish that is so smooth that is certainly doesn't require a top coat. The one component primer is much rougher and looks totally flat is a nice product as well. I'd compare it to the Cortec-373 stuff but I do not know how it would resist salt water spray. I'd ask Stewart about it and if in doubt, go with the Cortec-373. It has been tested thoroughly.
Keep in mind though. It's not just the spraying - that would be easy. If you decide on the interior priming the surface preparation is more important than the primer as any primer won't work if it doesn't stick to the surface.
I spent a significant amount of time just prepping and priming, with the emphasis on prepping. You need the maroon Scotchbrite pads and some surface cleaner/degreaser. Cortec-440 is a good product for that and also provides a surface modification on aluminum and steel that by itself will leave the metal more corrosion resistant than without. You have to scruff up every surface you intend to spray as the primer won't stick well enough to the shiny alclad surface. Just handling the part during assembly after spraying will rub off the primer if you didn't prepare the surfaces well enough.

Have definitely been-there, done-that on this one. My first RV was a 7A slo-build for which I used NAPA 7220 self-etching primer.
Pluses:
- easy to point and shoot at individual parts,
- very fast drying.
Minuses:
- expensive ($200+) by the time you buy enough cans for a whole plane;
- even with vigorous preparation scuffing and MEK or naptha cleaning, 7220 will not bond well enough to aluminum to keep it from being scuffed off in day to day use once the plane is flying, or easily wiped away with MEK.
- Looks lousy when it starts getting removed by abrasion in areas of constant mechanical contact.
- Top coat interior paint applied over the 7220 doesn't have any better abrasion resistance than the primer, and constantly needs to be touched up.

Didn't use it on the second or third RV for this reason.

For the next 2 RVs -- the -10 and the -12, which is currently sitting in a garage located less than 100 feet from the edge of the Pacific Ocean, it had to be iron-clad protection. For that Nobel AKZO two part epoxy primer (available from Spruce) is I think the primer of choice.
Pluses:
- Once bonded to aluminum, impervious to moisture and solvents; basically same stuff used on Boeings.
- Fast drying (about 30 min to assembly) though not as fast as rattle can primers.
- Easy to mix up (I used the little bathroom size Dixie cups as disposable measuring containers),
- Easy to apply in small batches using a cheap touch-up spray gun from Home Depot or Harbor Freight.
Minuses:
- smelly, somewhat toxic though not as toxic as two part urethanes;
- have to let it sit for 30 minutes before spraying
- have to clean gun with lacquer thinner or equivalent solvent after every application.

The full nine yards would include a phosporic acid wash, followed by alodyne wash, but in my experience this isn't any more durable than just scuff with scotchbrite, clean with MEK, and spray the AKZO primer. And in my experience phosphoric acid and alodyne conversion adds many (read: up to hundreds of hours) to the build process when repeated for all of the various parts needing corrosion protection.

Recognizing this is the stuff of primer wars, at least this particular $0.02 worth of advice is informed by using these methods on real RVs that have flown hundreds of hours and whose routine wear and tear experience has convinced me about a middle path approach using epoxy primer that is reasonably economical, reasonably fast, and provides terrific adhesion and corrosion protection.

YMMV,
-Dan Masys
RV-10 N104LD, RV-12 N122LD