Yes, I do three coats total. But I'm not using Campbell's. I'm using Mohawk Ultra Clear gloss, which is OK for self sealing and I'm sanding the crap out of the first coat. Like Stic said, the dull is not good for a sanding sealer. Sorry I should have been more specific.
If you are using dull, which is loaded with fumed silica (flattening agent), a vinyl sealer will be a better choice. Then you can shoot 2 top coats. You don't want to build too much finish with CV or it could craze on you.
Mixing small quantities can be a pain in the a$$, especially measuring the catalyst. These 1ml oral syringes are real handy and you can get them cheap at a local pharmacy.