@SirNuke All of the comments saying spray foam are technically correct - that is the easiest way but it will look like orange crap. Some people mentioned steel wool - avoid that because it rusts and will end up looking like orange crap. Find some “excluder mesh”, which an inexpensive product sold to the pest control industry - it is a nylon mesh with reinforcing fibers…think Brillo pad stiffness. Stuff the gap to fill it then use silicone sealant to finish it off.
I would say the expanding foam would still be preferred. Just don’t go crazy with it. Then before it’s fully cured, cut it back flush. Wait for it to dry then caulk to cover/seal.
That’s a good suggestion, I was looking at stainless steel wool and wasn’t finding a lot of great options.
Spray foam on the inside. Silicone on the outside.
Duct seal.
That’s pretty universally what I have seen used here. This stuff for those unfamiliar.
Spray foam is generally what’s recommended. Be conservative with it though, it expands a lot and can push wires and cause other problems if you use too much.
With a hole sealer