I need to rig two objects together that follow one another the same way a train car or truck-trailer rig would. I’ve Googled for days and have tried several different constraint and skeleton options but haven;t been able to figure this out yet. Help anyone??

Here is a train rig system I did a while ago.  There isn’t a lot of description on the page, but the scene files are linked there, and hopefully they can be of some help.
http://kaap.us/tutorials.php?entry=woodTrains

The approach I took was to constrain two locators to the track, one for each axle.  The track is a series of NURBS curves, but you could use a single curve much more easily.  The geometry for each train car would pivot on the rear axle, and be aim constrained to the front axle.  To maintain the distance between the cars, I relied heavily on carefully parameterizing the track curves that the locators moved along.  By knowing the curve length and its parameterization, I could assign parameter positions to each locator to maintain the correct placement on the track, according to the lead car’s movement.

For a truck-trailer, it seems like you would either need a curve that the truck should drive along, or you would need to have some programmatical way to make the trailer follow the tractor around turns—an expression or dynamic simulation.  That could get tricky.  I would start with the same idea, though—move the trailer’s pivot to be at its rear axle, then aim constrain it to the hitch point on the tractor.

-T