Kent, one thing that I have noticed with my weighted bumper (see attachment) is that it can get caught on the ground when the ground has a fast rise behind the PT. Not a big deal, but stuff will scrape some. Yours sticks out farther and may be more of an issue. I believe that this is why they slope the bottom of the PT up in the back. I can put upto 120 pounds on it, but 65 pounds seems to be enough most of the time. I rarely take off the 65 pounds as I like the way the machine backs up hills and generally handles with the extra weight.
I like your box in that it can also hold tools, chains, etc. You might consider carrying some commonly needed stuff there all of the time.
Bob Rip