Isn't much you can do as you do not own the land. Your also not there full time so even if you had so sort of document to say you had rights to have trespassers arrested your just not there.
Grin and bare it is about it.
My wife asked if I was going to post no trespassing signs at my UP deer camp. I told her no I live 6.5 hours away so could not catch ANY one any way. also the people who would trespass on land not theirs would just use the signs to set the place on fire.

Al