hi can metal tech filler be applied over rust seal and any ideas on what to do on welded panels when you cant paint rust seal when back of panel is not reachable\ thanks

Yes, you can apply metal tech filler over RustSeal. There are three effective ways to top coat RustSeal with fillers effectively so that the coatings bond & fuse together. 1) Apply your filler once the second or final coat of RustSeal is dry-to-the-touch and does not leave a fingerprint (usually 3-10 hours depending on temperature and humidity). 2) Let the second or final coat of RustSeal fully cure (at least 24 hours), scuff the RustSeal with 300 grit, then apply your filler. 3) Let the second or final coat of RustSeal fully cure (at least 24 hours), dust the RustSeal with Fusion Self-Etching Primer (http://www.kbs-coatings.com/fusion-self-etch-primer.html), let the Fusion cure for 30 minutes, then apply your filler. You can feel free to choose the method that will work for you. As for the panels that are hard to reach: Cavity Coater is ideal for those applications because it easily gets in to those hard to reach areas and coats them to prevent rust. Check out the directions for Cavity Coater HERE. Please let us know if you have any additional questions.