[AMSAT-BB] Waterproofing antenna-mounted pre-amps

I recently built two low noise amplifiers (2 m and 70 cm) for satellite work, hoping to mount them right at the antennas. They are in small Hammond die cast aluminum boxes. To mount the boards inside, I had to drill several 4-40 thru holes through each box. I’m worried about slow water seepage through these screw holes. Can you suggest a good way to seal them?

Thanks!

Joe K1MNY