Michaux State Forest campgrounds have vault toilets and the sites are well-maintained. I went in late fall and was the only camper at the area I stayed in. Unfortunately you cannot reserve sites online and it's a little tricky, but it's free... 

Camping is free in several areas throughout Michaux State Forest (as well as other PA State Forests), BUT you usually need to have a camping permit (also free) and you can only stay in designated campsites. To obtain a permit, find out where the designated sites are, and/or find out what designated campsites are available, you have to contact the State Forest District Office for the forest you would like to camp in. 

More info can be found here: 

https://www.dcnr.pa.gov/Recreation/WhatToDo/StayOvernight/BackpackingAndPrimitiveCamping/Pages/default.aspx