King of the Hill solo strategy

I've been struggling to get 5 skulls with King of the Hill, and I wasn't finding the online videos from the usual suspects helpful. In particular, the Elemental Lords were flattening me around wave 31. I think it's largely that I can't seem to master the crossbow. It's not all that difficult to get headshots, and yes, they do a ton of damage compared to my standby the Stone Staff, but it's a single target weapon. The way the Lords break down into smaller stuff was giving me far, far too many opponents at once, I kept getting overwhelmed when I had to deal with 2-3 Lords at once. The smaller enemies in the early waves were rough as well, since headshots are slow spraying at close range is pretty ineffective compared to the Stone Staff.
Anyway, I managed a way around my limitations. I'd like to sing the praises of the Spike Wall which I hadn't really appreciated before. It's a physics trap, and more to the point it's the only physics trap that works on the really heavy stuff (Lords, Mountain Trolls), and it works reliably, unlike spring traps. It's amazing on stairways, because stuff gets flung back and tumbles all the way to the next landing, even the big guys. Generally speaking 1-2 Lords simply cannot get past a Spike Wall assisted by improved tar on this map, either in the front hallways or the two rear stairways overlooking the acid pit.
Only a steady stream of stuff will defeat the Spike Wall, getting past while it's still resetting. Several walls - a set at each landing in both front and back - can defeat really large groups of big stuff. If there are only a few left, it's pretty common to see a Troll or Armored Ogre get smacked, fall down to the previous landing, and then get smacked again to fall down another stairway. A pair of doors in the rear corridor will often fling a medium-heavy like a regular Troll or Ogre right into the acid pit.
Lighter stuff is a problem, so I put grinder / push trap combinations on the front stairways, and simple push traps on the rear ones. For the first 25 waves or so, I didn't have anything get past the final landings (the ones with the explosive balls). I didn't lose any rift points at all until wave 41. Most people put their primary killboxes on those final landings, and it's far more restful when most orcs find it a struggle to make it that far.
For flyer defense, I put Autoballistas on the sides of the two causeways. Since they're pointing up, their 180 degree arc of fire covers the entire flyer hall, effectively doubling their range compared to a ceiling mount. Eventually, though, the flyers get too tough for them. It was the flyers who eventually wiped my out on wave 57 - the only way to use physics to kill flyers instead of straight damage is ice, and I didn't have room for the ice amulet. There are frost bats in those waves anyway, and they're immune.
No video, sorry. It took me 3 hours to get to wave 57, and I'm too burnt out on that map to try it again in a video.

@Juicebags-I think I read they fixed the crash issue on this map in a recent patch, not 100% sure about that tho.
 
Gus, that ballista placement works wonders! I did try them on the ceiling but found they weren't great there, so putting them facing up on the sides like you said was a great improvement - coupled with two webs pointing up on the rampy bit where they fly out, 5 ballistas on each side, kept the flyers at bay and that part was totally self sufficient till wave 43 where I finished,  overrun by orcs, so thanks for that. :)