Didn't need it. It's not that it's tight to the skin, drysuits are actually pretty loose.
The problem was that once you get the feet in (which you have to do first because of the booties, you have to bend in a strange way to get your arms in, and then it's even harder to get your head even in the right place for the neck hole. I'm not much of a contortionist, so it was a bit tricky.
It's definitely watertight. Pretty incredible. You have to burp the suit by bending down and holding the neck flap open, otherwise you end up looking like a balloon.