I thought of this thread a little over the weekend as I did a 'Gambler 500' event. I agree with tcora that a stock 986 can be okay if you are careful and choose you line well and if the roads are somewhat maintained. With or without mods, know where your critical points of the undercarriage are and put the car where they will not be impacted. If impact is inevitable make it as slow and controlled as possible.
Wheels and tires - small wheels, tall tires with pressure as appropriate for terrain. This Mercedes was driven carefully, but debeaded tires twice on Saturday.
The Volvo had old street tires and lowered the pressure on the rears for traction. Eventually the exhaust had to be cut to keep from dragging. The fan shroud had to be trimmed after the core support was impacted enough that the fan was striking the shroud. The transmission cooling line was a low point and was damaged enough for a moderate leak. By the end of the day, the Suburban was towing it.
My Boxster is still loaned out, so I took my Prius. It has a 40mm (1.6") lift, spacers, and tires that are far beyond the recommended size. It was awesome, but still would have been awesome with the maximum recommended size (all terrain) tires.
If you want a car that two people can sleep in with HVAC running, search YouTube for "Prius camper". and keep the 986 for street.