have at least 2 portals, both reasonably far away from the summoning stone and don't go near them during the fight unless you are retreating.

Making hidy holes under/behind big rocks is not that useful, Moder's attacks will pulverize even big rocks in only a few hits.

Considder digging a safe hole UNDER Moder's summoning stone, it is completely indestructable and can give you protection while your stam/HP reg. I do this and it works, Even put a Portal in there when I can, but the way the stone is shapped underground you can't dig out under it very much. I always bring a stone cutter bench and put a bunch of floor stones to act as a roof. teh cut stone seems to have more HP than raw stone.

Keep a chect with frost resist potions next to your respawn point to use if you need to recover your wolveskin cap form your marker.

Have a good AOE weapon like Stagbreaker with you, one hit will clear the ice crystals Moder's breath attack leaves all over the place.

Good luck.