Magnetic paint is useful only where the area is large and the load small (e.g. temporary attachments to a display wall). Someone on one of the forums did some experiments recently with a few products and found that, even with multiple coats, performance was poor. Add to that it is very expensive stuff.
Adding magnetic storage to existing single figures on thin circular bases isn’t easy. It is one of those things that you need to think about before basing, sometimes even before painting, to get the convenience of magnetic storage without the extra bulk. If you want to add the convenience then I’d suggest that you need to decide to accept the extra thickness or do without.
Try a bit of 0.5mm Plasticard or a bit of cereal packet loosely glued under the base and see if it really is as bad as you think it will be.
Rebasing on galvanised washers is a possibility that will work well – thickness about the same as you have now and weight down low for better stability. Line storage with magnetic sheet. The problem is the dreaded re-basing !!!
Tony of TTT