I have a mikuni adapter for the shovelhead. Bought the support brackets. During tuning it in it coughed and blew it off several times. Bought a mikuni filter designed for the shovelhead that clamps on. Now with the support brackets it goes nowhere. Couldn't pry it off if you tried. Those adapters should grub screw or clamp on. IMHO

 

The OP has a Twin Cam and the stock air cleaner mounting is much more sturdy than on a shovel, the bracket mounts to both heads and the carb is securely trapped and can't go anywhere, be it the stock CV or a Mikuni with the adapter.

The problem the OP experience is that the actual air filter he uses is not supported, and the metal mesh that is the core of the filter breaks down from engine vibrations. This is particular to Mikunis own filter for Harleys, other air cleaners have supported filters that don't carry any load.