Old and Tried
My 62 year old certified airplane isn't primed. It's lived most of its life in the dry states like Colorado. The only corrosion it's ever picked up was due to six months tied down outside of Philadelphia. The thee years it was in a hangar on the west coast, three miles from the beach, did nothing.
I agree with this. My '61 Debonair had no primer inside and no corrosion up until 2012 when we parted ways. An argument could be made that Beechcraft started using primer on the interiors of it's aircraft in the late 60's, and therefore, if it was the right thing for Beech, it should be right for me.
I imagine the primer debate will continue in perpetuity and I simply have my opinion, which is that for the internal structures, I don't use primer and instead use a product like Corrosion X after the build, and then re-spray every one to three years (depending on your climate), which will provide active corrosion protection rather than relying on the passivation that primer by itself brings.
The big advantage of an anti-corrosion spray is that if you did NOT prime the interior of the airplane, or you bought an airplane without primer, you can still provide corrosion protection after the build.
Here's the thing, even though my certified airplane was primed, I still spray it internally every two years. It takes me 1-2 hours to do and uses a little over a quart of the stuff to do the whole airplane, and the stuff gets into everywhere. If you have corrosion or a loose rivet, you will soon know where it is, as the CorrosionX will provide a dirty streak out of wherever the corrosion was. The full benefits and description are available on their website, but I will add that it does a great job of keeping the interior parts shiny, stops corrosion in progress and presents further corrosion - it's main purpose. If weight is an issue, this is a lot lighter than primer (an RV-12 only needs about a pint of this stuff).
It does have it's minor drawbacks, which are - if you spray everything down FWF with the cowling off, better have a pan under the airplane as all gook and corrosion will come off and drip to the floor. And you shouldn't use it within six months of painting, as paint will not adhere to it and it will penetrate and then come out of every imaginable spot and it works through rivets and bolts. As an aside, it's really good at making the engine bright and shiny and is recommended for electrical components as well.
In direct response to OP question, I do not regret
not priming the interior of my airframe. I did not prime the wings, control surfaces or fuselage of my aircraft, except where it was called for in the directions - generally only where non-alclad parts were joined, and certainly all ferrous parts.