Installing shocks is entirely custom work and it seems like every trailer is different. On my Aluma-Lite, there was room between the frame and tire to install the shocks outboard of the frame. On my Jayco, I had to install them inside the frame. When you go inboard, all sorts of things like holding tanks tend to get in the way!
Personally, I like the shocks with "stud" type mounts on both ends. I build a bracket out of 1/2 inch plate to replace the lower plate that goes under the spring and extend it out and to the side slightly. I drill a 5/8 inch hole for the shock stud and grommets. For the top, I usually build something out of 1/4 inch angle iron with the 5/8 inch hole. I have run the shocks straight up and down on most trailers, but I have installed than at an angle too. Straight up and down give better control, a little harder ride, and are usually easiest to build. Angled shocks give a better ride, allow using longer shocks that are easier to find, but are not possible to install on some models.
You have to take into account the full suspension travel to make sure your new shocks and mounts do not hit on anything... like the sidewall of a tire. Also make sure there is enough travel in the shocks so they do not bottom out on top or bottom when the suspension is moved to it's limits. I recommend you get an idea of how long a shock you will need and then go buy your shocks. Based on what you buy, make the final decisions for where to put the top mounts. I recommend small diameter standard shocks. I find heavy duties are just too stiff for a travel trailer and the larger diameter make them harder to install.
Shocks I have used include from the front of a 70s Dart or Aspen, Front from old International pickups, and front from late 50s-early 60s Ford and Dodge pickups. A good parts store will have a listing of the specs of all the shocks they sell. A little study time should get you something that will do the job.
Take your time and THINK IT THROUGH before you weld anything into place! It is a major problem to cut things apart and change them later!!!
Steve