Hello group,
In case anyone wants a more hidden hitch than the as-sold 'hidden hitch' that hangs out beneath the bumper, I have another solution for you... Just use the bumper - if you have a welder to add on the parts that is.
I was able to find a 2.25" hitch coupling at Tractor Supply Company, and they are available at harbor freight too - or get an adapter for 2.25" that could work just as well. You also need some 1/4" bar for the safety chain hookup, like 2 feet or so.

You also need some hinge for the licence plate and I used a magnet glued to the back of the plate to hold it down to the hitch. Just planning to lift the licence plate and put the hitch in, there's clearence to put the trailer on, and hopefully the cops don't care since the plate is on the car, and you have a plate on the trailer too - just put it back to stock when you aren't towing something.

And don't forget a trailer light adapter that you can buy - think it's a 4-3 adapter or some such thing. Or you can build one like i'm going to do. This adapter is needed to turn off the high brighness brake lights to flash the turn signals (when your brake is on and your turn signal is on) since we don't own old cars that used one light for both functions like the trailer does. I'll attach a schematic once i've made sure my circuit works, and I remember to put it up here - though I doubt anyone is going to make their own when they can go buy one that's all done for $30.

Removing the rear bumper isn't too bad, the rear lights are the biggest pain since there's a plastic pop-in that I was only able to get off by putting about an 8mm deep socket over and pushing it side to side to get it to release. And the trick to the side bumper clips (white slider section on the frame side) is to push the bottom of the bumper forward and it will release easier.

Cut a notch in the top of the bumper down to where there's a reinforcement welded on at the center toward the back of the car (see pics). I cut until there was about 1/8" left before the reinforcement went horizontal just cause that's how deep my cutting wheel went. Just make sure it's level and line it up to where you want it to come through behind the licence plate - do double check before welding. With the bumper back on the car you can mark for where to cut out by holding stuff in place. I used a soldering iron that has a temp control and it takes a good 15 min or more to get the cutout as shown. I had to widen the hole on the right (since i'm right handed) to get the receiver pin in there more easily - but there's guide lines in the plastic on the inside you can follow to get fairly straight lines too.

Once aligned, weld the hitch part on, paint it etc... Here are some pics of the so far untested version of the hitch. Keep in mind that this is not a true class I hitch, no 2000# capacity, i'd keep the max weight to under #500 or so but i'll report back once I get a trailer and test this.

Fire off a question if you have any, and good luck.

 

Haha, that's pretty slick.

 

Followup with the wiring of a build it at home 4-3 light converter. Here is the schematic, should be easily viewable if anyone wishes to copy it.

I didn't mention it above, but the 7.5A sunroof fuse in the front is connected to a pink wire with a blue stripe, comes out 3 pins up from the corner of the connector that's on the bottom side of the fusebox toward the center of the car - the larger connector - ohm it out and you'll find it. I'd change this fuse to a 10A to handle a normal trailer load, that depends on the trailer too, LED lights on that would make things more efficient.

As for vehicle wiring, there's a ground splice for all the right rear tail lights just over the right rear strut mount - good for the trailer ground. Or go to the front just behind the door for the ground bolt location, since you may need to take all that plastic to run wiring (I did). There's space on the right for mounting the box behind the trunk side lining - and a rubber plugged hole right there to run wires in.
The lights are very easy to wire to - the black(er) wires are ground (going to that splice & bolt mentioend above). As for the switched 12V for the lights => parking light is orange with blue stripe, left turn is blue, right turn is blue with red stripe, brake is red with a orange stripe on the left or green stripe on the right.

I didn't take a pic of everything in the final box, but it's all installed and tested with a dummy load. Just beware that the heatsinks on the FETs are switched 12V for the lights, and I had one bumped to touch a ground on the board which blew the fuse during my first test... But that means that the fuse works before killing anything else right.

Good luck to anyone that wants to recreate this, msg me if you need further information.

 

Had no issues getting it inspected, the light control mentioned in earlier posts works just fine, and no questions about the car licence plate being tipped up.

The trailer is quite jumpy, since it's rated for 2000# (doubt it could carry that) but its got way stiff suspension - which i'll be modifying shortly. In the short term there's like 25PSI in the tires to soften the bumps.
I've attached a pic of the complete setup. Another issue is this particular trailer is nearly neutral balance with the bike on it, so it's on the rattly side with minimal tongue weight.

Notes - if you get the 4x6 trailer like I did from tractor supply, it's required that you move the tail lights up to keep the licence plate from digging into the ground when you tip up the trailer. Though where it is kind of gets kicked when moving around.
I put on some posts so I can see where the rear of the trailer is, otherwise it would be horrific to back up when the trailer is empty.
I'd also recommend soldering the wire connections, since the ground on mine was horrible, with half the wires not even under the crimped connector.