I have the bowie and the standard (not been able to track down a discontinued mini at a decent price), and played around with both stuffing the handles and covering them. I tried bicycle inner tube for a handle cover, wrapped paracord, and both together. Rubber was sweaty, sticky, deteriorated and distorted easily, paracord was just as bad if not worse as it was also too bulky. I also played with stuffing the handles, but wasn't happy with that either. If you are planning on doing any light chopping with it, you either need to empty the handle beforehand and repack after which is a PITA plus there's a chance of losing something, or you can use it full. If you use it full it will not only rattle and risk damaging the contents (dependent on what's stowed in there), but it will also shift the centre of gravity backwards into your hand making it less effective at chopping. Now both of them are just plain empty handles, and to be honest I've found that much better
I had one and found the steel to be very soft, guess they have to or it'll snap when used as spear.