Yeah, that looks like way too new and nice of a trailer to be adding on to. Even if you were a pro with all of the equipment in the world at your disposal it will still likely be obvious that you hacked it up and put it back together. Since it is newer and in nice shape, what I'd do first is get a price from a local dealer to trade for what you want - Not saying you should do that, but at least see what the difference is, and then start subtracting out the materials you need to buy to re-do yours. You may find that it's just not worth it to start cutting and welding. I'm pretty well equipped and capable, and I wouldn't cut into a nice trailer like that. My 20 year old homemade one - well, that's another story.