So, spoiler alert: I got The Slopes working with v21.
I had to decimate the hell out of it and reduce it's poly-count so I could make tris and quads suitable for collision in v21's static engine without taking up an assload of datablocks. There's just one main problem- With a map as big and complicated as this, there's collision issues involving offset raycasting.
To make it clear-
player and bot collision works fine and is 100% functional. This bug seems to only affect things which are bound by raycasting.
When a vehicle is used, it won't follow the terrain in the same way that player collision or bot collision does. Flat areas work fine, however once a vehicle goes over a hill with an odd angle, the car will either sink into the ground or drive above it on a short 'invisible poly'. What's super odd about this is that if I were to drive up the area again in another direction, sometimes I'll collide with the terrain just fine.
I've had this bug before when I had first made my first buggy-mess of a map, "
Kerumi Valley", where I had dubbed the mysterious error as "Phantom Poly". This is because I noticed that with every tri in the map, there was a "Phantom Tri" that would accompany it, making it into a quad that would only effect of what I suspect is raycasting, as only ghostbricks, bricks, and vehicles seemed to have the error. (I don't know how or if it affects weapons/tools.)
I have reason to suspect that Non-Planar Faces might be causing this issue, as bent-quads seem to also possess this bug. I'll look into it soon. However for now, I just want to know if anybody else has gotten this error while working with staticmaps. If you have another solution or recommendation, please reply with your thoughts.
(Or if you're just excited that Slopes is coming to v21 then scream your face off.)----------
EDIT: Oh yeah I forgot a download link.
Here's a temp version of the project, not in its final build quality, but if anybody wants to play around with the map before it's finished, go ahead.