Absolute First Thing to Do Before You Even Think About Going Off-Roading

Put a flex pipe between the header and the catalytic converter. You can get one off a junk car, ebay or here:

http://www.performance-curve.com/index.asp?PageAction=VIEWPROD&ProdID=417

Most front wheel drive cars use a flex pipe or a ball joint between the engine and the exhaust system. Each time a car accelerates, the engine tilts back. You can see that clearly when you rev the engine. With a rigid exhaust system, it would be like taking a 6 ft extension wrench and prying at the exhaust manifold each time you accelerate. The exhaust bolts won't last very long that way. Flex pipe allows the engine to rotate in its mouts without putting stress on the exhaust manifold.