CHIME!
Like 08H3 says...their are some nice fire-trails throughout the LBL. Most of these are dirt/mud with some mild rock/stream crossings...nothing extreme. Depending on the time of year you may have to cross some fallen timber (or winch it off the trail). All of these fire-trails radiate east & west off the main paved road that runs north-south thru the island...so its difficult to get truly lost. Most of the trails dead-end into the shoreline of the lakes, Barkley to the east and Kentucky to the west. There are usually 3 or 4 nice camping spots at the end of each trail. Buy a back-country camping pass (around $15) and you're free to drive/camp where ever you wish. You must stay on the trails, and watch out for horse back campers. These trails are for horse-back or licensed vehicles only (no quads). You'll need to be 100% self-sufficient (firewood, toilet paper, water,etc.) as there are zero amenities at these spots.
If back-country is not your bag...there are many campgrounds in the LBL. Some are full-service, while others are pit-toilets with a water spigot. The full-service campgrounds take on-line reservations but its a complete mess (worse than Obama Care's website!), so I recommend just showing up in person...around $20/night. The primitive campgrounds are first-come, first-serve and they have a self-serve honor system of payment on-site...around $10/night.
Turkey Bay is the dedicated Off-road Park inside the LBL. It has a separate admission gate, and I cannot recall the price but, its very fair. It reminds me alot of the Badlands or Rausch Creek, and you will have to share the trials with dirt bikes, side-by-sides, and quads. It has everything from mild to wild...lots of steep hills, mud, rocks, etc. The trails are clearly marked but, in true ORP fashion...its impossible to tell what trail is what. So just hit it and have fun. They have a primitive camping area available inside Turkey Bay if you choose to stay there.
More tips:
The entire area is "dry"...so bring your own beer/wine/whatever.
No fuel anywhere in the LBL....gas-up at Grand Rivers (north entrance).
Firewood is inspected for ash bores...best to buy it locally. Its priced fairly.
Bug repellent is a must during spring/summer.
Many areas are prone to flooding in March-May (makes for fun wheeling).
The Bison park is a drive-thru and its pretty cool.
If trail-running alone, have a back-up (winch, come-along, hi-lift)...vehicle extraction is EXTREMELY expensive if you get stranded.