What causes blisters with vac hanging

So I am seeing that there are a variety of factors that contribute to these blisters. What do you do to make sure you don’t get blisters? I’ve read some people tape excessively, while others use other techniques. So please share what you feel causes blisters and what you do to stop getting them other than stop hanging.

Make sure any remaining air is fully vented. Reduce time of individual sessions and reduce amount of weight until further conditioned.

Ok, so what are some of the ways you fully vent the air?

I believe that Monkeybar has instructions on his web site. Assuming, you have a newer cap with a vent hole:

Place cap securely on the glans and roll down the leeve.
Pull up on the hook with one hand as far as possible. And hold for 15 to 20 seconds
Release the stretch and push down on the cap against your glans
When fully pressed down, roll the sleeve briefty down over the vent hole while still pushing the cap down. You may hear some air rush out
Quickly roll the sleeve back over the vent hole.

Nothing I’ve tried really works for long sets apart from loads of careful wrapping.