Yer killin' yerself, Rudy, yer killin' yerself.
The reason why I don't jump in all the time to answer primer/paint questions is because the subject is so "large" and the more we talk about it, the more confusing it gets.
Each specific question begs a specific answer because of the various chemical "intents" of each of the products, and things get more confusing when you consider that no one product is designed to do something without
another product within the brand or system.
You started this thread with way too general of a question, so I'll throw in some general ideas to help get you in the right direction, and keep in mind that I am talking ONLY about RV's, what they are made of, and what we can do to protect them or make them pretty.
A. The inside surfaces of our RV's are protected from corrosion by being coated with pure aluminum. That's what "alclad" means. This pure aluminum is more resistant to corrosion than is the aluminum alloy it is applied to.
So, generally, Van's statement that you do NOT have to add any further protection to the inside of his kits is correct. However, there ARE reasons why we probably should go further and do some additional corrosion protection, and that's because we strip away areas of alclad when we machine prep the panels for riveting, and we also (probably) scratch parts of panels as well. So for a "perfect" aircraft, most of us do some kind of additional corrosion protection if nothing more than using an Alodine "pen", or maybe just priming the edges where all the riveting is done.
B. Once you decide to add additional corrosion protection to the inside panels, you are then faced with way too much information about chemistry, methods, brands, procedures, etc. This confusion leads some people to search for the "perfect primer" that is absolutely better than everything else. After all, since there seems to be lot's of choices, then it stands to reason that there MUST be a "best" choice, right? (Hint: There is no "best" primer or system, but there are several good ways to go.)
C. There are three subsets of base metal protection. They are:
1. "Conversion" chemicals that react with the aluminum chemically. Examples of these would be the ubiquitous Alodine, or the Sanchem products and others. These are the "messy" products that require preprep chemical cleaning and thorough rinsing. If you enjoy giving your dog a bath, then this system is for you.
2. Primers that react with the aluminum chemically. An example of this type would be Veriprime and Zinc-Chromate, but there are others.
3. Primers that don't chemically react with the aluminum, but sprayed on properly CLEANED aluminum, add long term protection to (inside surfaces) almost as good as using a complete paint system. As a group, these would be the epoxy based primers
A couple of additional points here are that, even though the above 3 types of products add protection to aluminum, they are ALL designed to be used UNDER a topcoat, and that goes especially for the conversion chemicals like Alodine. Left uncoated, conversion chemicals offer at best, only the same protection as alclad which is why some guys just use an Alodine pen to cover scratches rather than do the whole panels.
Primers in the Zinc-Chromate and Veriprime class (Zinc-Chromate has been replaced by safer and better products like Veriprime) are also designed to be topcoated, but do offer a very minimal amount of a moisture barrier (but not much).
Spraying a primer of the type mentioned in item #2 on top of a conversion coating described in item #1 is a waste of time and may even cause a LOSS of adhesion over time because #2 primers REPLACE conversion coatings as a "process". These are the "self etching" class of primers.
Another point is that enamel based and lacquer based primers are totally worthless for the job.
D. Don't get hung up on brands because any of the well known brands offer excellent products of the types noted in the preceding paragraph. HOWEVER, once you choose a brand, stay with it. Chemical formulations are generally similar for similar products, but manufactures spend lots of big $$$ in research to make sure that each of their products work like they are supposed to with their other products. Unless you consider yourself a "pro" and have knowledge of cross brand compatibility, stay with the same brand all the way to the final paint finish.
Over the years, I have used most of them including Dupont, Sherwin Williams, PPG (Ditzler), and a couple of foreign brands. In the end, I settled on PPG as my only "system" so whenever you ask me a specific question, I will usually phrase an answer around PPG products. However, you won't go wrong with any of the major brands as long as you stay WITH that brand to the end.
E. For me to tell you the "best" way to prep/prime the inside surfaces of your RV is like telling you that the guy I voted for in the last election is the "best" president for our country. He is (Bush), but lot's of people will disagree and tell you otherwise. That's the way it is when discussing primers.
What I offer here is simply MY thoughts on a good way to go with inside priming so here we go:
1. If you don't prime inside at all, your aircraft will still be flying years after your next of kin inherits your RV.
2. If you do want to prime, don't make it a big whoopty-do; make it as easy as possible on yourself, yet do it in a way that will give you REAL benefit and not just a good "feeling" about it.
3. Remember that we are working with brand new alclad panels. They are not recycled, or used, or have any corrosion problem that has to be "fixed". Because of that, and in my opinion, that means that we don't really HAVE to get down and dirty on pre-prep. That means that if you want the easy way out, you can go with a self etching primer such as Veriprime and not have to use a conversion process. As I mentioned earlier, you do NOT want to use a conversion process UNDER a self etching primer such as Veriprime. All you need to do is to properly clean (CLEAN)... (did I mention; clean?) the bare aluminum before spraying.
4. If you will be hangaring your aircraft, then Veriprime only is an easy, and effective, way to go. However, Veriprime isn't as good as a moisture barrier as is epoxy primer (such as the PPG DP/LF), so if you think your RV will be spending most of it's life outside, then I might consider using a conversion coating (again, Sanchem 6100 seems to be a bit less messy than Alodine), but then spray a coat of epoxy primer over it. Once cured, the epoxy primers are a better moisture barrier (but still not as good as if it were top coated with urethane paint... but don't go there).
I'll even say that, because our parts are brand new, and if you want to use epoxy primer, you don't really need to use a conversion process first. Spraying the epoxy on top of brand new and properly cleaned (no wax or grease residue) alclad will be way more than enough long-term protection.
Now, let confusion reign.
Highflight