Mark,
We built our trailer about two years ago and if I had it to do over again (maybe someday) I would make a few changes for sure.
I pull a 6'10" x 16', steel decked, dual 3500 pound axle, bumper pull trailer. I thought I wanted the "extra" width but after pulling this for 70k plus miles, I think a narrower one would of worked.
I also put the hot water units on the rear of the trailer. Which will be moved to the front soon.
On top of the rails, we added 4' expanded metal sides with a double gate at the rear. These hold my ladders and have toolboxes accessible from outside of the trailer. When this was built I was on the road more and wanted the security ofthe "semi enclosed trailer" but without the wind resistance of an enclosed one.
Personally my next trailer will be a gooseneck but that would require a 4 door Powerstroke to pull it. I am doubtful my wife would fully appreciate why I would need a new truck. So...that one will have to wait.
Good Luck
Harlyn