I learned to use high quality duct tape as a remedy for blisters, etc. until I used it as a precautionary preventative. A heel wrap across the instep and a tie down under the arch and across the instep wrap protects against heel abrasion creating a smooth surface for any existing boot slippage. Similar to wearing a nylon liner sock (idea from the old days) but liners always chewed my feet worse than the main socks. An extra advantage from duct tape, and I'm not sure why it happens but, when I did get blisters and added tape for relief, the blisters healed over the next couple days (week long trip)?? Chemicals in the tape? YMMV...