Thanks for the tips on T nuts. I agree that they require some special care during installation. I've used them in the past and had no issues with them coming out. I use a different method of installation that you do. The T nuts I use come from Lee Valley in the 1/4 and 3/8" sizes. I normally use the largest size I can to get more strength. I will use 1/4" for the woofer mount. I use 3/8" only for spikes or foot installation.
To install them what I have done in the past is this. I drill the body hole as recommended. I then put the nut in position and give it a little tap to make marks where the prongs will go. I then pre drill small pilot holes for the prongs. This keeps the prongs from bending. I then use a drill press with a piece of 5/8" round in the chuck and press them into the wood. You could also use a bolt to pull them in. I apply some Weldbond or PL Premium to the barrel of the nut and the prongs. This method seems to work well and doesn't put a lot of stress on the threads or the nut itself. Baltic Birch is a hard material for installing T Nuts. The pilot holes help ease the installation considerably. In MDF the pilot holes prevent the MDF from swelling around the prongs.
I haven't had any trouble with rotation when using this method. You need to make sure you don't over torque them as the thin wall of the nut isn't as robust as a regular grade 5 nut would be.