There are some awesome CGs (very rustic) in the Washburn area in the Chequamegon national forest. There is one called Birch Grove CG. The sites are large and can easily take a TC. It stretches between east and west Twin lakes. We stumbled upon it while doing some exploring.
You may also ask this on the RV parks, Nat parks and state parks forum.
Not too sure about the off-roading part, but people do use ATVs at times. You might want to check the WI regs. The DNR is pretty picky about our pristine waters and forests. The beauty and serenity will make the trip worth it.
2011 Adventurer 910FBS truck camper,Torklift tie downs,Fastguns & Wobbl-stopprs
2012 Dodge 3500 DRW 6.7L CTD,4x4,LB,CC,auto,3.73 axle,General 17" on/off rd
2008 Lund 1825 Explorer Sport,115 Merc,9.9 kicker,Torklift Super Hitch,42" Supertruss
USAF ret E-9&E-7