There is really no worse job than finish sanding prior to Sealer/Base/Clear. Every square inch of the Cab (in this case) inside and out must be super smooth. Since the high build primer lays down bumpier than the 400 grit paper used for final sanding, everything needs smoothing.
This is literally a very painful proposition because the only way to get into all of the grooves, crevasses, etc is with your fingers. After a few days of this the tips of your fingers feel like someone is sticking needles in them all the time. I then resort to good old Duct Tape. Tape up the ends of your fingers and keep working. I can properly smooth about 24 square inches per day on the inside of the cab. Very slow going and very tedious. I do this by tearing off about 6 inches of 400 PSA sticky and fold it in two.
http://devestechnet.com/Images/D50b01068lg.jpgUnder the dash is the worst. I know nobody will look under there, but I will know! There is no escaping that, so I do everything inside and out with the same standard. With 4 titanium rods, 13 screws and two plates in my lower back, this type of work brings tears to my eyes! But no matter, it's all part of the process.
The good news is, I can stop at 400 grit now that PPG has a Sealer that completely heals 400 without wet sanding and adding the possibility of rust into the mix. The interior will get a single stage Urethane paint, while the outside will be base/clear. I may go back later and do some clear to the dash, but I am hoping I am happy with the gloss of the single stage.
Anyhow, just wanted to share that. If you haven't restored a vehicle from the bottom up yet, you will appreciate knowing whats coming! Or not.