First, there is little to be afraid of with modern 4WD systems. The $3k up front is just about the same $3k in value up to about 10 years old. The fuel economy is unmeasureably different.
However, if you haven't needed 4WD in the last 50 years of driving, you probably won't in the next 15. Towing an RV means more weight on the rear axle, more traction that unloaded. Today's traction control systems do a pretty good job in most situations. I highly recommend whichever OEM's limited slip or locking differential. That's a performance bargain.