Snake keeps doing things I don't intend, though. Like if I try to turn in a crawl while next to something, Snake starts to stand up. It's stressful.
This is going to sound insane, but there's a way around the awkwardness of the crawling animations:
When crawling with the third person camera, the Snake model is always checking collision with everything around him all along the length of his body. Trying to rotate Snake around in a tight spot will often cause issues because his feet or length of his body will collide with objects around him and the game will keep trying to streamline the animation so he doesn't just pinion spin on the spot.
HOWEVER
When in first person mode, the actual collision volume for Snake is a single point near his head. You can be locked in a tube, unable to turn around in 3rd person, but just pop into first person, spin the camera around, come out in 3rd person and he will have magically become facing the other way.
Interestingly enough, you can actually use this to hide from some guards, as when you are in 3rd person, your feet can be sticking out of a corner and a guard can see you. If you pop into first person, your feet disappear (as your only collision volume in first person is your head) and they can't see you.
So in summary: when needing to turn or, especially, turn around while crawling, going into first person, spin around then come out of first person.
FUN FACT:
In MGS5, the camera position when going from 3rd person to first person is actually the center of Snakes body, around the hips. This creates idiotic situations where you can have Snake's head over the ledge while crawling on the roof and then go into first person and you will be a foot back from the edge. Additionally, if the roof edge has a raised lip, you can position Snake's head over the lip, go into first person, and the lip will be blocking your view. Irritating as hell.