I say always get permission and if you cant find the Owners go to the Tax office and see who owns the land and contact them, On a Side note you have Access to a Truck and Trailer there is a big world out here where you can get metal yeah you may have to pay for some But that is what scrapping is all about. Don't let that Pile of stuff in the woods Stop you from from looking for other resources. Thats just my 2 cents.