Maybe remove the Immunity:Web that doesn't work and instead make the Sewer bonus also work in vermin filled areas like the Spider Caves and the Moldmire.
Do not remove the immunity: web, as it works sometimes. I'd add immunity entangle as well as some web attacks are actually entangle.
Compared to many of the other ranger favored enemy perks, vermin is a bit watered down as is. Web is a long lasting AOE spell. It might work the very first time you're hit by it, but you're probably going to make at least two saves before you leave the web area.