With NO trailer connected, load up the rear of your vehicle and drive around. Does the rear of your vehicle feel like mush? re: Too soft. If yes, get HD shocks installed in the rear of your Vehicle. Remember that shocks don't lift a vehicle. They only reduce the speed of up/down movement (when going over deep bumps). Many folks sometimes call it a "bounce test". If bounced more than 2 times, then replace shocks. And if replacing, replace with better then factory grade shocks.
With loaded vehicle (as if going on a camping trip) WITH trailer connected, drive around. Does the rear suspension of your tow vehicle feel like mush? re: "2 bounce test" thing. If yes, then install HD shocks. Do keep in mind that if upgrading with HD shocks (like HD Bilstein @ http://cart.bilsteinus.com/
), the "loaded down" feeling will feel much firmer. But, it might feel "too firm" during empty load. Thus, don't over buy HD shocks for your vehicle. Sometimes, too HD rating replacement isn't good. Especially if daily ride - that runs empty most of the time.
With NO trailer connected with vehicle's rear loaded (as if going on a camping trip) and vehicle's rear sags down too much, simply install Timbren SES units. They are like air bags without compressed air inside them. Thus, no worry about air leaks. Simply install and leave them. Or if you prefer air bags, then install air bags (which are adjustable) instead. Timbren and/or Air bags are made to reduce vehicle's rear sag when NO trailer is connected. Timbren SES units or Air bags are made for Vehicle.
With trailer connected and rear of vehicle goes down too much, I would install a WDH - with properly sized bars. A WDH System does more then reduce vehicle's rear sag. It also transfer some of the trailer's tongue weight to the Tow Vehicle's front wheels. Not much weight transfer but on slippery roads, every little bit counts. WDH System is make for Trailer's tongue weight.
If wondering, I installed Timbren SES units under my previous vehicle and my current vehicle. When loaded down and NO trailer connected, they work great. Especially since both of my vehicles have factory "soft suspensions". And, they also work great when trailer without WDH system (like my utility and boat trailer) are connected as well. But for my heavy tongue weight RV/TT, I always use a WDH System (with properly sized bars). Both do work together - if adjusted properly.
Long mumblings short... You may need to install HD shocks (to eliminate compression speed), you may need to install Timbren SES or Air bags (for Vehicle rear support) and you may also need to install WDH System (to support RV/TT's heavy tongue weight). I installed all 3 upgrades in my previous Vehicle and it was money well spent...
Note: For your Dodge 150 (with soft factory suspension) and 23ft TT, I would buy/install a WDH system (with properly sized bars). I might even install Timbren SES units if vehicle had too much sag with NO trailer connected. And, I'd do the "2 bounce test" to determine if new / replacement shocks are needed.
Hope this helps...