Search for Allenfahey. He's the resident painter and has gone over this a few times in other threads. Bknbronco is basically right, but some people like to etch prime first, Then WAIT for the acid to evaporate, then seam seal, then prime, sand, then primer sealer. I personally like all my primer sealer sticking to primer although you can shoot it directly over seam sealer. Depends on how much money and time you want to spend. This is from 3M
Directions for Use
1. Always apply over automotive paint or primer when applying to metal. Applying over bare metal will not provide enough corrosion protection. Acid etching primer is not recommended; if used, be sure to allow to fully cure before applying seam sealer, or residual acid can weaken the bond.
2. If necessary, clean and dry surface with 3M™ General Purpose Adhesive Cleaner, PN 08984. Do not use an adhesive cleaner until the primer has fully cured.
3. Cut nozzle tip to provide 1/4" diameter bead. Puncture foil seal in base of spout. Knock out end seal at the bottom of the tube.
4. Place in 3M™ Professional Caulking Gun, PN 08993 and engage ratcheting mechanism.
5. Apply desired bead width and tool to final appearance, if necessary. When sealing is complete, disengage rachet to stop flow.
6. Wait to dry before applying paint over the sealer (if desired). Thicker beads of seam sealer will take longer to cure before painting. The stated dry time before painting is based on a 1/4" bead at 70 deg F.