Nice job! I considered doing the same to my trailer, but I also needed to increase the length by 5' (I'd already increased it by 2'), and I also would have had to change the axles to accomodate the additional weight.
By the time I figured my parts bill, it was cheaper for me to buy a bigger trailer. However, I admire a guy who isn't afraid to design and then execute his plan. By the way, what steel did you use going from the trailer to the truck? I think I went overkill with the trailer I had built. I had them use 19 lb 12" I beams on each side. /forums/images/graemlins/blush.gif It looks like you used about 6" stuff which should be more than plenty for your sized trailer.