Marlin,

 I've never seen the connectors you speak of, but from your description they sound like a do-it-yourself dream. Building bulk cable assemblies you have cost constraints, so for volume use, those connectors probably are not practical. I did use heat shrink tubing with adhesive on the inside for special applications. That sound like what your talking about. Good stuff, waterproofs and keeps shrink wrap in place. Again very expensive, but worth it in the long run.
 I can't help on the plug in problem. That's a weak point for sure. The cables I built either had a twist/lock type connector, or used threaded bolts to lock in place. Vibration on the plug in connectors is the killer. Best I can suggest is keep the male/female ends clean and lube with dielectric grease on regular basis. I found that on the female ends, you can use a little LIME-AWAY to clean the insides of the end. Use a small brass brush, the kind you use to clean firearms. Clean male ends the same way. Another thing many people do, is let the trailer connection hang loose and the end collect moisture and get corroded. Some of the newer connectors come with a rubber cover plate, or else you use a small baggie and secure shut between using trailer. More often than not, wiring issues on trailers are in the connectors, or a poor/no ground. All can be eliminated by a little preventive maintenance ;)