Can't answer for Diamond but of course I have an answer in general.
I think it has more to do with the dealer who handles your custom order, than the brand. Most brands we used to know are now just a brand owned by an investment group. Mine is a Cargo Craft, while there were a few minor issues, I would order from them again. Pretty sure they are still privately owned. They really stepped up to correct the issues, very satisfied. In hindsight, I guess I was a bit picky, but it was a lot of money to me. It has proven to be an excellent value, and has towed great behind two different tow rigs. I developed a leak last year, but in the fiberglass nose cap near the center marker lights. Not the fault of Cargo Craft. Simple fix. The rest of the trailer has remained water tight since 2012. I recall one of their marketing points was a water wash test rig for every trailer.
http://www.tnttt.com/viewtopic.php?f=42&t=48345Another brand made in Tennessee that I would consider is Homesteader, again via a dealer with experience in custom orders.
https://homesteadertrailer.com/Lately, I ran into this manufacturer, they actually posted to my Twitter page regarding my trailer. I have kept up with them, and really like their approach to building, and custom orders. It's a long way off, but the exchange rate is pretty good right now, might reach out to them, and see what they can do. Aluminum or steel, custom orders, seem like a really good crew there.
https://www.canadiantrailercompany.net/