Doctor Benjamin Franklinstein has invented an anti-gravity device for the movement of soldiers.
But seriously, I have been making movement trays out of black styrene with thin rare earth magnets sandwiched between 2 sheets of plastic. I made 20 2 inch by 2 inch trays for infantry (holds 4 miniatures) and have enough plastic left to make 11 2 inch by 4 inch trays (which would fit 3 of my cavalry), but need to order more magnets before we can move cavalry on the anti-grav devices.
The black plastic is ok as is, but I think I'll try painting some trays green to better match the minis' bases and my terrain pieces. Have to see if the paint rubs off over time sliding minis on and off the trays.
3 hours ago