I think that calm rage won't be a good idea because the biggest problem you have is how to make enough dmg on the rangers before the melee force you to go in bat form. Without book of evil or other summon to slow them down it takes them 3 rounds to reach you and with 36 mana you can cast poison skull r2 the first 5 rounds.
In my game I managed to clear all 3 stacks in the castle's basement which was really hard but at least I didnt have to rely on insane luck.
The first stack against the spiders I used the battlefield to tank them. There was a close spot in the corner where i left my vamps, then I cast r2 Book of Evil next to them so that thay could be attacked only by one stack. Since the spiders dmg is poison the book could tank 3 stacks for fairly long time, enough to get mana for second book.I think it lasted for 8 rounds because at least in 2 rounds I had 2 books on the field.
The second fight against the 3 big stacks of snakes was the hardest. I had to make the book to tank and dmg the royal snakes alone so that it wont die in 2 rounds. I used 1 scroll of magic shackles when thay were close to avoid the snake bite, and 2 slow scrolls on the other snakes. Once the royal snakes were dead I got enough mana for second book to reduce the numbers of the red snakes and after that it was easy.
After the second fight I finally got to lvl 6 and with r2 Concentration and r1 Diversions the third fight was much easier.
Then the real challenge comes in whitehill where you have to kill at least one of the guards and each of them have like double the size compared to the human guard in Shelter, while you are still with your good old 2 Vampires
So I used rage pot for 10 rage before the fight.
The first round the inquisitors skipped their turn thx to diversion which is good becouse thay were the strongest range and the other 2 already wasted one of my vamps. Then I used the jelousy skill from blackie on the 1 big stack of melee and thanks to some bug thay remained red even after the statue disapeared. That way slaughtering all the mean priests and archers for me
After that it took me 230 rounds to finish the guardsmen.
Thanks to this bug it all went fairly easy which is good because i didnt want to start all over again with phoenix spell.
Whithout the bug I dont think it was slightly possible to win any of the fights with my setup of 34 mana. May be with 40 mana and 2 rank2 books from start and alot of luck it would be more possible but those rangers were really scary.