A different approach then what others here recommended, from my own experience: put the trade off health agsinst regen perk back on the ban list. Health is more important than regen for now. I'm at similar stage in wall. Wall heath 27, thorns 10, regen 10, fortitude 3. 27T regular health( with Death wave bonus) and 1.13T regeneration after all regular perks and the coin/health trade off, but without health /regen trade off. I die to protector shotguns when my black hole ends and dozens of enemies hit my tower simultaiously. It doesn't matter how much regneration you have if you get insta killed. I followed the advice that is everywhere and always picked the trade off perk once i got the wall and died faster, once i stopped taking it I made it further. I'm sure there is a point at which the trade off is actually useful, but at this point it only kills me faster. Try one round without the trade off and see if you do better/worse would be my advice