How to beat Treasure Island Iron Challenge on impossible walkthrough

How to beat the Iron Challenge of the "Treasure Island" level on impossible.
Specific level info:[TO DO WHEN I HAVE TIME]
General DLC and video info:
The new DLC for Kingdom Rush Vengeance - Pirates is finally here! I have recorded some tutorials for the new levels, as some of them are pretty hard.
I use only free towers (and the DLC one, because it's awesome) and heroes (Asra, you can use Lucerna to make it easier, but will probably have to modify the strategy a bit) and try to make my strategy as consistent as possible while requiring minimal skill from the player.
I play on the impossible difficulty and without the Pit Lord upgrade, to minimize RNG. So, as you will presumably be playing with it, the levels will only be easier for you.
I also intentionally do not micro Asra or my units efficiently, letting them die even when unnecessary. This is, again, because I'm trying to make my strategy as simple as possible, and as consistent as possible, with only very simple micro, such as moving Asra to poison a lone enemy, without tight timing needed.