So a bit more on sanding primer. As I said earlier I do not sand primer with a sanding block, but always by hand. This is critical when you get down to the end. I always wet sand primer at the outset, but change over to dry at the end. The problem with sanding wet is the more opaque areas become somewhat transparent and it's hard to tell the areas to sand, which results in cutting through.
Final sanding dry can be a real pain due to the paper loading up, but it's worth it. I just sand a bit and knock the buildup out of the paper. When you are getting down to the end, you will be just sanding the little opaque areas in between the transparent spots. A lot of times I am just adding pressure on the paper with one finger. One other thing is to stay really focused when you are near the end or you will constantly be cutting trough the primer.
I felt I could get a bit more primer off the wings and have them down to 15 grams that was added per bipe wing. In some spots, just a couple more passes of paper would cut through. That's a lot of area for only a 15 gram buildup. Put something in your hand that weighs 15 grams. You can hardly feel the weight.