I particularly like what I did with the lights. Keeping in mind the 23" sides, I added a vertical wing (for lack of a better term) with a 2"x 4" u shaped channel welded to the front side of it. This way the lights have protection both front and back. With two holes cut in the wing I mounted two round 3" or 4" truck trailer lights stacked vertically, one upper one is a brake, signal, tail assembly and the lower is a backup light, which I've been glad to have more than once. This wing assembly is welded to the side of the trailer about 12" from the rear so the lights are well protected. I think only a piece of horizontal pipe could punch one out. A similar assembly is on the other side of the trailer.
I also added a pair of brackets underneath the rear to carry a pair of ramps. As to fenders, I agree that they usually fall off or at least look like they are about to do so. I made mine out of the same steel that I used for the body of the trailer. They are welded to the side of the trailer with an additional brace centered above and between the tires.They are sturdy enough for me to set or walk on, and I'm not a lightweight.
I used a drop axle resulting in about an 8" step from the ground into the trailer. The drop tailgate can also be used as a ramp for some things. The tailgate is mounted with a long rod serving as a hinge pin so it can be removed if necessary. The drop-axles were purchased at an RV parts place and are rated at 3500 lbs. each.
Another little touch I like is having the safety chains up off the ground during storage. I welded a single link from the chain (a ring or etc would work) on the bottom of the hitch A frame back toward the trailer at distance that would let the S hook hook into it for storage.
I would prefer to back a tandem axle trailer any day to a single axle unit. It has less tendency to try to wander all over the place. I can usually put a trailer where I want it, but, I find it easier with a tandem.
I like your idea about verifying that your towing vehicle jack will lift the trailer. I had not thought of adding a pad to fit the jack.
Thanks for the work you've done on the page. I hope these comments are helpful.
Way Up North, on the 45th Parallel
where the air is clean and CRISP!