Electric brakes, not surge brakes. I really, really wish that someone would make electric "disc" trailer brakes instead of just drum brakes.
The trailer jack on the front? Drill 4 holes in the pad so you can bolt a swivel castor wheel to it to move the trailer around on concrete if empty. Stake pockets on the side rails and make removable sides that interlock and slide into the stake pockets. Bright white backup lights on the trailer - both sides. Backing it up in pitch black areas is no fun without lights.
A place to mount a swiveling crane to pick up something that you might not want to drag up on the trailer?
Too bad it's already started, but making the trailer out of aluminum will save a buttload of weight and allow you to have more payload.
I have an aluminum Triton trailer, and it has grooves where tiedowns can be slid to position, and tightened down. 1/2" carrige bolts, heads go in the slots. Not only on the bed but on the side of the trailer too. I wouldn't trust them for a vehicle tie-down, but for just about anything else they work fine.
I have a dovetail car trailer. I made ramps that are in 2 pieces with a center brace. Extra long to get a car that is low ot the ground on the trailer without scraping it on the trailer. Ramps slide down on 2 square posts on the side of the trailer for storage and have a large wingnut/washer that hold them in place. Wingnuts have holes drilled thru one wing and are close enough together that a padlock with a long hasp can be used to lock them together. No way will they get stolen off of the trailer. If the vehicle has ground clearance, only 1/2 of the ramps are needed.
Aluminum trailer has a 4" tall rail by 1/4" thick running around the bed. I made a set of ramps that can slip over the rail for loading ATV's from the side. It's got two pieces of angle that are spaced about 1" apart to keep the ramps from sliding off of the rail, but can be moved anywhere forward/back to accomidate different width axles.
Car trailer just has 2, 24" wide solid diamond plate runners for where the tires go. I bought some aluminum diamond plate to cover the open area in the center. Used large nutzerts in the trailer frame to attach the aluminum with bolts. If needed the aluminum can be removed without too much work.
On the car trailer I welded a piece of thick walled tube with a 7/16" dia center hole on each rear corner. Drilled/tapped the tube to fit a 1/4"-20 thumb screw. Tube is vertical. I put a 3' piece of 3/8" steel rod in each one with a red reflector on the top that faces forward. Backing up I can tell exactly where the dropped dovetail is now. Thumbscrew holds it in place, thumbscrew is long enough that I run it all the way in and tighten it down when the reflectors aren't in place. Just in case, I have a couple in the trailer box for spares. I mounted the license plate on the rear of the driver side trailer fender and put a light over it. No way will it get knocked off there. I DO like the flip mounting bracket if mounted anywhere else tho. Great idea.
Laugh, but if your truck doesn't have a backup camera, these really help getting the trailer and ball aligned if you are by yourself.
https://www.etrailer.com/Hitch-Accessories/MaxxTow/MT70043.html