We build two size's trailers in the same shape m416 size and a 4' x 6' bottom of the box dimension "Gen2" trailer.
But we can build larger, we charge $150.00 set up fee for changes that deviate from our size then just extra cost of addition material for the build.
www.Sierra4x4Trailers
I love your trailers. I would be interested to know what it would cost of one like the picture below but with a 5.5' x 8.5' with a lid to match in the same color scheme or flat black in place of the OD, and spray in liner.
I would also want a 6000lb - 7500lb axle with brakes so I could use 8 bolt wheels without adaptors.