Can I apply Cavity Coater into the back side of the fuse and relay panels under the hood to prevent moisture from causing corrosion in the connections?

Yes, absolutely. You can spray the back sides of fuses and relays with Cavity Coater to prevent corrosion which commonly happen under the hood. That is an ideal application.

Please be sure to read thoroughly the Cavity Coater Directions and let us know if you have any questions.