Over the years I have built two fairly large flatbed trailers.  The first one I built was a dual axle unit.  It was built somewhere in the mid-70s.

In 1995 I designed a larger trailer for hauling vehicles.  Below is the first cad drawing I made in the design process:

It was designed as an 18 foot bed with triple mobile home axles.  The tongue was separate from the frame and was bolted to the frame so that the bed would tilt, or a new tongue system could be designed to make it a goose neck trailer (never did make that modification).  The photo below shows me loading one of my 50 Oldsmobiles on the trailer using the tilt function:

In 2017 I decided to rebuild the suspension system from the three mobile home axles to two 7000 pound Dexter axles with very heavy duty 19.5 tires and wheels.  The mobile home axles were not all that robust and the tires became illegal for use on anything besides a mobile home application.

The photos below show me turning the trailer over with my gin pole trailer and the modification with the two axles.

In early 2025 I decided to rebuild the tongue structure to make it a much stronger.  That includes going to a 2 5/16 hitch and reinforcing the structure with 1 1/2 x 1/2 inch strap.  At the same time I lengthened the tongue 3 1/2 feet so that I could lengthen the bed the same amount.  The photo below shows my messy shop and the trailer tongue in the process of being modified.