Very low indeed Roughrider, be carfull you dont hit any debris in the road or mount a kirb/sidewalk, you could bash in the bottom front of that lovely big box.
Any reason for the added box holder uprights sticking up? Looks as though that could be a little dangerous! I'd slice them off level with the frame.

All that's left to do now is wash yer wheels - give the frame a lick of black paint, and that'll be one cracking little trailer

Wish I could source out a nice big box like that

Regards
Tom