Anyone have this? I don't have a dealer anywhere near me and I have no idea how you pick the correct size. I sent them an email with my question, but no reply yet.

It's an extremely warm jacket, you won't have to wear much under it to keep warm in even the coldest temps....I'd get whatever size jacket you normally wear.

I have noticed that Sitka gear clothing normally runs on the small side.  If you are border line between 2 sizes I would jump to the next higher size.

I'll second that! Skinny guys like Curt don't notice this. I wear a large in most jackets, my XL Sitkas is snug with zero room for anything thick under. Just ordered new one in 2XL.