Yes, both the Markland and the Hitchdoc attach to the upper frame in the same manner. You do have to drill the threads to run a longer bolt and a nut to secure the uprights. The main purpose of the uprights is really just to hold the back end of the hitch up, so in that respect you might be able to get by with the thinner stock, but I'd still prefer the 1/4". The uprights do, on a smaller scale, help divert the forces exerted during stopping and accelerating, up to the upper frame so that all the force doesn't have to go through the lower saddlebag mounts. This is where your idea shines, because you've tied into the floorboard mount/frame area instead of just the saddlebag/crash bar area. But it also is a concern, because of the material used. Think of it like this. You've got a piece of coat hanger a foot long and a piece 2 inches long. It's the same material, but which one is easier to bend? It's leverage, I know, but that's the problem as I see it. This is also why I think adding in the piece I mentioned might help firm up the unit.
The rear fender support, in my opinion is barely adequate to support the fender. With the amount of potential movement of the hitch, at least as I see it both in your current configuration and what I've seen with a Hitchdoc and the Markland, I'd rather not have anything tied to the fender/bodywork back there. That's one reason why my trailer wiring connector is only attached to my hitch (for both hitches) and not the saddlebag, fender, etc. What you could try, and maybe you have, but without the 2 braces you have going to the fender support, but with the rest of the hitch bolted up solid, put your foot on the side of the ball and push. See if you get any side to side movement. With the saddlebags off, do you get any movement and is it just in the hitch, or is it in the saddlebag mount area as a whole. If you conservatively figure the weight of the trailer and contents at 300 lbs, then do some fancy ciphering, you come up with some big number I'm sure, LOL. I'm betting I was pulling close to 450 when I tried hooking an F150 with the trailer, so I know what the Hitchdoc can take.
I just want to make sure you're safe out there.
Edit: For the wiring, I made a bracket that attaches to the hitch that incorporates the connector for the wiring. You could do the same, depending on how many wires you're using, etc. Since I am using a 6pin connector, the kit comes with a bracket to mount the connector. I used that piece and integrated it into the bracket I made for the Hitchdoc, and for the Markland, I just made the entire unit. Don't have decent pictures of either at my disposal since I'm at work, but could dig some up if you're interested. On the Hitchdoc, it was mounted here:
![Image](http://i49.tinypic.com/bgxxzc.jpg)
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"If a man made it, a man can fix it." - Steve in Sunny Fla