I had made a 22-35 PS built that was running the map in about 21-22 minutes and i decided to give it a try on campaign and its pretty fast, im sure theres some ways to make the build phase quite a bit faster but 6~ minutes is nice i think
do the entire build in build phase and then run 2p tower boost on hint 3 + upgrade and upgrade everything until the boss wave(sometimes u dont max everything out but its stil faster than not upgrading and running 1p until boss phase)
on boss wave i run tower booster + builder warden + 2 monks with huntress guardians one buffing each stack
the gas trap is kinda needed to make the built consistent i think sometimes the crystal takes damage without it, probably would be solved with an ogre but i cant do that in the first build phase and i dont feel like doing it in the 2nd so i just put a trap
video of setup and stuff here: https://www.youtube.com/watch?v=VMjMNqK6r8I