Free: Contests & Raffles.
100% public land, national forest, just off 1500 USFS Road
Just keep walking and mind your own business. Do you report all speeders to the law? Who knows why it's there or whose it is. Could easily be a handicapped grandfather that's taking his grandson on his last year of hunting before dying of old age and got some odd permission to build it and put it up for the season. If it's not affecting you or your family, move on and worry/report something that actually matters.And you're right, only southerns hunt out of box blinds for whitetails.
Regarding the legality on NFS lands, have you guys witnessed what kind of modifications rock climbers have made? Trails of expansion bolts have been drilled, even in wilderness areas, and the NFS (in practice, not necessarily in policy) doesn't raise an eyebrow.