As much as I like magnets, sometimes they’re a bit annoying to use. I have been assembling a fleet for Dystopian Wars (Vive la République!), and fitting magnets to the tiny gun turrets looked like too much hassle. Enters magnetite. I bought a bag of it on Amazon a while back, and today I put it to good use:
Step 1 - drill a hole.
Step 2 - add magnetite (yes, I am just as messy when I brew coffee).
Step 3 - press down, and gently remove excess using a paintbrush.
Step 4 - add superglue and wait for it to dry.
It holds! Result! (obviously, there is a magnet fitted inside the hull, but that one was easy enough to install).