I don't know where in MO you live, but, there are a bunch of trailer manufacturers scattered about. I think you'll have to have something custom built to take the twisting force. You won't realize how much stress that will put on the trailer, until you load it up and raise it to dump. I know it seems minimal, but, just having a WB setting in the front corner of a trailer will cause twist. A standard mowing trailer is built as cheap as possible (C-channel everywhere). I'm not sure on shortening it up, overall. But, if you just moved the axles forward or ran a spread-axle to get support as close to the insert as possible, you might be able to get away with a lighter build. For sure, you'll need at least a 6" tube frame with tubular crossmembers and tubular curb rails. It'll need all the support you can get under it. You'll have to go with 5200lb axles, as well.