My Thoughts on blisters
I have got a few glans blisters. First few times from overdoing it with a vacextender and then during dynamic water pumping for a fairly long duration under a high max vacuum.
I believe surface moisture on the glans skin seems to promote blisters. I now use baby powder (corn starch) on my glans with a condom on top and held in place by a silicone sleeve during water pumping and do not get blisters even though I dynamically pump for over 12o mins in the range 3 - 10” Hg I attribute that to the drying action of the corn starch, If you are air pumping you might just try the baby powder by itself.
When I got blisters I used Vitamin E cream to help healing. Being uncut helped as I used my foreskin as protection during the healing period - 1 to 2 weeks depending on the size of blister.