Applying permanent mask to player animators walk

Hi, Hope everyone is well!

I would like to apply an animator mask to the top half of my player so that the top half is constantly masked with an animation that is holding a gun while walking. There is a death animation also so it cant apply a mask when the death animation plays.

The animator for the player: https://gyazo.com/8aa9e8b7511669b31b5f73c2b0a2e3cb

I have already setup an actual upper body mask, Im just not sure how to apply it this way. I have done it before where I have multiple layers and the second layer has a mask but at that time I had different triggers that called different animations so those were masked with different gun holding positions.

Anyways, overall im quite lost so any info would help and if I need to supply info let me know.

Thanks in advance! ~J