I build mine using as much travel as possible. I could design and build anything and my last two are solid axle leaf. I did this because of ease of repair. In my opinion only one of the independents work properly. My leaf's are about 45" long, KYB gas shock about 8-10 inch of travel and air bags to level it out based on load.
I can run about 45 mph an a moderate dirt road and have (accidentally) caught air. Off set ruts and rocks, the trailer takes them smoothly. I run low tongue weight, center the axle under the box. The axle to tongue match's my vehicle length and width. The trailer follows my track perfectly. My M-100 trailer has seen hard core trails for a couple of decades. The teardrop, moderate trails.
If I was going to do anything trailing arm wise, they would be at least 20" long, coils with poly air bags inside them. Shocks would be as long as possible. On that note, I've been using KYB, early VW bug. My M-100 weighs about 1k loaded and my teardrop about 2k loaded. My long dirt road driving, the teardrop has been overheating the shocks. I need to come up with a larger diameter or possibly a reservoir.
Hitch wise, multiaxis or go home. In my opinion all of the ones on the market have a common flaw. They all spin 360 degrees. The ones I make will only go about 160 degrees. My M-100 on two occasions tried to flip on me. Both times were slow and both times were a fluke. If it did happen on both occasions, I would have been forced to drag the trailer quite a ways before righting it.