I'm here from the not-too-distant future just to mention that it appears the Harbor Freight 5x10 trailer will soon be no more!
Not sure exactly what happened. It seemed like there was a fair bit of anticipation for it when it was first shown at SEMA a few years ago, but then it was delayed for a year or two, and apparently it wasn't selling in high enough quantity after release, so it's now on clearance.
I'm a bit of a Harbor Freight deal veteran so I waited for an opportunity to buy one. Wasn't sure if I would use it for a teardrop, my ATV, or something else. On first release, it was priced at the announced $1000, but then I watched in horror as it almost immediately rose to $1200 - assumably as a result of tariffs, inflation, and general supply chain uncertainty. Not exactly uncommon, as automakers do this all time too (looking at you, Ford Maverick and Slate Truck).
After the price jump, I all but wrote it off and was inclined to wait and weld my own chassis some day, a la
@Tony Latham's recommendation. However...
Just a couple of days ago, I had a chance encounter with a Redditor who had a 25% off "We miss you" email coupon. Half-jokingly, I asked if I could use it. To my delight, he actually sent it right over and said he had no need for it. I have a few semi-large Harbor Freight purchases in my queue at any time, so I got on the app to see how the coupon could be best spent.
Out of curiosity, I pulled up the 5x10 trailer product page, expecting it to be at least $1200 still, if not more! But it was actually only $900 now, already discounted 25% off the previous price on clearance. That got me excited. I almost lost that excitement immediately when I saw that it was out of stock at my usual store, as well as the dozen other locations in my metro area... except one. It was a 45-minute drive, but small price to pay. I called them to confirm they actually had one on hand, and they were down to the very last one. They gave me a 2-hour courtesy hold and I raced up there yesterday afternoon.
So, I am now the new owner of a Harbor Freight 5x10 trailer kit for $675 out the door. Hard to beat that.
It had to go right into a storage unit since I'm in the middle of a cross-country move, but in about a year, I expect to start the build in earnest. Will try to share as much as I can here once I start making some progress!
(I can braze copper pipe pretty good but it doesn't seem to translate) anyway, I could make do with 5x10 but would prefer 6x12. Is this something regionally dependant?
Danny 
