Whenever i try i either fall through the map, or clip back into the map, and i can only crouch in the tunnel if i even do get in there, takes off a solid 5 seconds from my run

Idk for sure how it works, but I believe you must crouch during the fall damage animation, doing that will give you the crouch hitbox but with a high camera and high move speed which allows you to go through the tunnel quickly, it also lets you go under the gap near the exit without needing to crouch.

As for walking along that edge, I'm pretty sure it's just really precise movement along the outer edge, too far left you fall, too far right you clip back in, you need to be in just the right spot.

oml you just saved me hours of trying, i thought it was just you have to be super precise, thank you bro. no idea why i never though of that