Can I use seam sealer with Mastercoat Permanent Rust Sealers?

Yes. The best method we've found is to apply Mastercoat rust sealer first, and then a brand name seam sealer as directed. You want to ensure the rust sealer seeps down into the seam and covers to stop/prevent rust. Without it, the seam sealer will just prevent water. If you plan to topcoat, apply another coat of rust sealer over the seam sealer and then a topcoat such as AG111.