Having cocked this up on my own forks, I can offer the following advice.
1. Buy a dead blow hammer. Don’t use a rubber mallet, a carefully aimed claw or lump hammer is viable alternative.
2. Make sure the forks are totally decompressed before starting. Otherwise, you’re fighting a losing battle.
3. Screw the bottom nut on until it’s just proud of the damper rod end / air spring. You only need about 1mm clearance between the nut and the fork lowers, you’re just breaking the seal.
4. Hit it once, firmly. One solid whack with the proper hammer is far more effective than many nervous, puny thumps.
I actually bought a couple of spare nuts and some ordinary M8 FT nuts to minimise further thread damage. Of course, I suspect now the reason the legs were unwilling to come out is because the fork was shipped from the factory with no oil, but I digress.
Even with the official Fox tool you run the risk of damaging the threads. Doesn’t really matter how many turns of the thread are engaged (the first thread bears in excess of 60% of the load) so you’re really trying to give a controlled whack that’s most importantly delivered vertically.