Salting baits?

I must make room in the freezer so thinking of filleting a few mackerel and just storing the fillets.

I am tempted for try salting a few.

Do ye think it will work if I place the fillets in the salt bucket while there still frozen or do you have to do it with fresh fillets?

I think it would work better with fresh fillets, not sure that the salt could absorb from frozen water. In the past I have filleted fresh mackerel, dusted generously with salt but not "buried" them, wrapped in clingfilm and then frozen them. It seemed to toughen the fillets up a bit.

If you salt the fillets for an hour or two before you freeze it will draw a lot of excess moisture from the fish which in theory should leave you with firm baits after they thaw.
Never tried it myself but your suggestion is worth a try, will try it myself when I get a few fresh maks. I would give the fillets a quick rinse to remove any remaining salt before freezing and pat them dry to prevent them welding to each other in the freezer.