Kuiu zip-off base layers rock. They are quick and easy to put on and take off.
If I need a base layer for my legs, it has to be fairly cold. I currently have and use Kuiu's heavy merino ones. I put them on when it is cold and I am stationary for a period of time. They come off when it comes time to move. If it is really cold (to me) and I will be stationary for some time, I'll throw the ULTRA down bottoms on and if windy, then throw rain pants over it. They come off as well when it comes time to move.
For the majority of my hunting, the ULTRA top and bottom work fine for me in combination with my merino bottoms. However, I should have just went straight to the PRO series and called it good. For not much more money and weight, you get quite a bit more warmth.
In order of warmth (subjective due to differences in all of us and personal preference):
1. Peloton 118/Merino 145
2. Peloton 97/Merino 200
3. ULTRA down
4. PRO down
Other than keeping my WM bag clean, #1 serves no purpose for me. Grab one from #2 and #4. You'll be well covered (no pun intended).
Here is what someone once told me about the Kuiu down tops and bottoms and throwing rain gear over them. "It is like slipping into a warm sleeping bag". While this is not completely true, there is still some truth there. You can absolutely achieve similar, or better, results with other brands.