Is Rust Bullet Automotive compatible with automotive fillers, fiberglass and primers?

Yes. Most body fillers, fiberglass and automotive primers may be applied directly over Rust Bullet. Two coats of Rust Bullet should be applied to the metal surface. The body filler, fiberglass or primer should be applied directly over the second coat of Rust Bullet between the time that the last coat of Rust Bullet is dry to the touch, about 2-6 hours, up to 12 hours. The previous coat should be dry to the touch and not wet or tacky; if there is no transfer of coating to a gloved finger it is safe to apply a filler.  If 12 or more hours have lapsed, wait for Rust Bullet to cure for at least 24 hours then lightly scuff with 150 grit; enough to break the glaze to create a surface profile. This 12-hour period is decreased in areas with high humidity levels.
Please note: Fillers have a tendency to absorb moisture which will cause further rusting of the metal and bubbling of the filler if applied directly to a rusted area that has not been protected with Rust Bullet. Rust Bullet works best when it is in direct contact with the metal.