I recently ordered a 4x8 flatbed trailer from Tractor Supply (currently on sale for $675 shipped to store from Ontario). It is a Sterling brand (aka Marathon) kit trailer. I've received the trailer and plan to assemble it in the next week or so if the temperatures warm up a bit; 4" of snow the last two mornings. It is sold by a number of US stores such as Home Depot, Tractor Supply and Northern Tool but I don't think they stock them.
This particular one is an all galvanized frame and fasteners and seems to be of very good quality. 1230# capacity with 1000# payload (230# dry weight). Just what I wanted to build a new foamie benroy to pull with my EV. It comes with 8" wheels which I will upgrade to 12" radials. I'll use an eight inch for a spare. I chose the 4x8 because it will be just me on trips.
What I like so far prior to assembly...
Dexter axle with solid tubing unlike the Harbor Freight and Northern Tool kits with C channel axle
Galvanized frame
Heavy duty fenders unlike the HF and NT trailers with cheap sheet metal fenders
https://www.westbrooktrailers.com/product/4x8-kit-trailer/?variant=4x8-Kit-TrailerModel-48-096-K08