Spring hunts can range from 80 degrees to 20 degrees in a matter of a few nights. The Kuiu Ultra Merino Wool 145 base layer is one of the most thought out base layer systems I have ever used. The zip off design so you do not have to remove boots is key. I work in Alaska and have had to use base layers extensively to stay comfortable. These are light, packable, & warm. You will not find a better base layer available.
Kuiu zip off ultra merino 145 base layer
Flat zippers for comfort and low profile under outer pant.