My EV builder is in full Divine armor so its walls are healing themselves, otherwise you will need to flash heal with a summoner.
This may work in campaign too, but did not try it.
I have 3 summoners with Range/Atkrate pets on the towers
1 DPS summoner with 2 eye pets on the central Crystal during waves. Flash heals reach all auras.
On wave 28 start, I used a TowerBoost monk to upgrade and buff.