If you only want the machine itself on the trailer, I see no need for anything more then a 3500lb axle and springs. Two axles would increase your cost initially and more for tires ect. I do not know how much the 400 weighs but I have seen plenty of Big blue 300, 400, 500 on single axle trailers that are factory and way more cheesy then anything you might build. I have a 1400lb machine that will be on a single axle and I am building it big enough for bottles, vice, chop saw and some tool boxes. If I was going to make a long trailer that would haul material as well I definitely would build a double probably with 5000lb axles....but for just a machine? naw
Tommy
Just make sure your weight is about 60-70% on the tounge.