It is a "state by state" situation....so you really need to research both Idaho and Montana's laws regarding this. Getting info here is a start, but far from being the final say so.
Seems to me that it would be simple enough to just make your permanent address at your cabin in Montana and then get driver's licenses from Montana. You are allowed to have property in multiple states, but can only be a resident of one.
Ron, Sandie, and Maggie May
2013 Tiffin Phaeton 42LH
2011 GMC Terrain SLT-2