On the outer edge of the driver's side door is a sticker with a lot of interesting (and arcane!) numbers printed on it. Look for the one that shows Gross Axle Weight Rating (Rear). This is the maximum total weight that the rear axle is designed to carry safely. You didn't mention the year or model details of your Dakota, so I can't look it up, but I bet the GAWR(R) is about 3800 pounds. Note that the 3800 pounds includes the weight that the truck itself puts on the rear axle, plus the contributions of whatever you put in the truck cab and bed, plus the weight on the trailer hitch.
When you get loaded up with the toys and the TM, you will be carrying a lot of weight on the rear axle, and I bet you exceed the GAWR, probably by a substantial amount. This is not good. A WDH will remove some of the hitch weight (a couple hundred pounds, maybe) from the rear axle, and move some of it to the front axle, and some of it back to the TM axle again. I'm not at all sure that a WDH will get you below your trucks GAWR-Rear, but it will certainly help.
Padgett notes correctly that helper springs/air bags will not reduce the rear axle load, and I am very much against their use, for reasons described more completely in the TM Technical Reference Library on this site. As they say, to each his own - but don't install them and let them fool you into thinking you have improved the weight situation. You haven't.
So how do you find out how much weight is actually on the rear axle? Best way is simply to weigh it. Load up your rig with all the toys, all the cargo, all the water you plan to carry, all the people that will be in the truck - load it as it you were getting to go camping, in other words - and take it to a CAT scale. They are everywhere
http://catscale.com/cat-scale-locator
For about $10, it weighs all three axles simultaneoulsy and individually, and gives you a printout. I highly recommend it, especially in your case.
Bill