A while back I got this great idea. Why not magnetize a playmat so that ships wouldn't slide around, or get shifted when some klutz (me) accidentally kicks the table?
I am proud to announce that I have succeeded in my attempt. Here's how I did it:
1) I bought 3x3' and 6x3' vinyl banners from bannersonthecheap.com using freely available high-resolution Hubble images for a cost of $51 shipped.
2) I bought one 4x10' piece of magnetically receptive "FlexIRON" material, 0.12" thickness, adhesive on one side, uncoated on the other, from magnetsource.com for a cost of $68 shipped. This was sort of a hassle because they don't have online ordering: I had to submit an email request and talk to a salesman on the phone.
3) I bought two 24-packs of 1" adhesive magnet squares from Amazon for a cost of like $5 shipped (yay Amazon prime)
I was able to lay the vinyl graphics on the adhesive magnetic material without much trouble (the 6x3 required some assistance from my roommate) and then trim them to size with a yardstick and a box cutter.
Then I put the magnet squares on the undersides of some of my ship bases. The only flaw is that they were too thin and couldn't really magnetically attach to the magnetic-receptive material. Doubling them up made them just a bit too thick (visible in the photo below), but with the magnetic attraction it's not a big deal. I am glad I kept some bases unmodified for play on other hard/smooth surfaces that don't have the magnets though, as they can tip just a bit on other play surfaces.
I tried modifying a large ship base with four magnets, one in each corner, but it's just too much magnetic attraction and I tend to pull the large ship off the base when I move it. The large ships are less susceptible to bumping/shifting anyway so I don't think they really need the magnets as much.
It's great for play--the magnetic force makes it so you can slide movement templates up against the ships without worrying about bumping them or moving them. Plus, magnets are cool. I have enough extra small bases to share with anybody I play against in casual play, so it's pretty nice. In full-scale tournament play the modified bases are probably technically illegal because the magnets extend past the bottom of the base--if I did some more research and could get some of the proper thickness they'd be officially tournament-legal, but that's more effort than I want to go into right now.
The results, in pictures: