JMB, I don't think i like the design of that trailer. I use my ancient trailer (1987) tandem axle every day during the landscaping season.
I think all of those tailgate and sidegate semi hidden catches will eventually haunt you. i have seen the pics of your loader/forklift machine and i know you are not bashful about working in muddy conditions. You will need to clean those catches often. Every day if moving your machine in wet weather.
i had a truck body with removable posts between drop down sides. I had to remove bolts and put back in when i wanted flat bed. That could get to be a real PITA, especially in winter freezing temps and ice conditions. I would never get another body like that.
The tie down points are a terrific dirt collector system. Give me floppy rings and solid welded bars along the side rails. I have ratchet type straps that i can hook up anywhere on my trailer. When I was having it built, i told my fabricator it was impossible for him to put too many tiedown pionts. as his assistant was welding all of those rings and bars, he constantly complained about my sanity. I have not spent the time to try to finally figure out how to post pics here on the FOG, but I have not seen too many trailers, if any, with as many tiedown points as mine.
I don't understand the suspension. From your pic, it looks like the only flex is tire pressure. Is it torsion suspension? That is probably better than leaf springs, but I am not familliar with torsion on a trailer. Those axles do look tough. I have 3750# axles (each axle)and I have already had to replace after first 15 years. I think mine are way over speced for the loads i carry. i don't think i have ever had more than 6000# gross, but the axles have broken down. I guess they get tired after day in and day out use. Your axles look to be much heavier. But I like leaf spring suspension.
Over all, if you can keep mud and other debris out of all those catches, and avoid denting or bending (that complicates hooking and unhooking those hidden catches) the tail gate and side gates, the trailer should give you satisfaction for many moons. Of course, if you get tired of it, you could always
put pontoons on it and send it across the pond to my place. :
Tinker