Hey guys,
I was watching a vid from BTP on Magnetic Movement trays that they want to sell, now, I don't know what they're selling them for but.... you can easily make these yourself in under a minute (assuming you have the material)

There's and easy way and a hard way

The easy way;

Use a Magnetic Vinyl 1/64" thick (0.020 for those of us that are in metric) cut it to size and adhere it to the inside of your Movement tray with 2 sided tape (either GW or home made) then glue steel washers on the bottom (underside) of your figures bases, making sure that they are thick enough to touch the movement tray without showing... and voila! Magnetized movement tray. BTW I saw the Mag vinyl sold on line - $5.00 for .020 x 12" x 24", that could yield about 16 4" x 5" movement trays

The hard(er) way (but more stealthy if you don't use a boarder)

Cut sheet metal to size 16 or 18 gauge thick should be sufficient, file the edges so they aren't sharp, Gloss paint the bottom (this makes it move smoother on the table), Paint the top what ever color you want (you really won't see it anyway), glue standard magnets (Rare Earth Magnets might be too strong, unless they're really small) to the bottom (underside) of your figures bases ... Now you can leave it that way for a "Stealth Mag Movement Tray" or for something more contemperary add a boarder and dress it up as you see fit

and there you go