The following cutting list uses readily available and standard size steel sections. Components are also standard and should be available from most trailer part suppliers or auto shop.
UPDATE - There is a couple of details incorrect on the following parts list - Part 2 - Drawbar Brace should show a quantity of 2 instead of 1 shown. Also there is an M20 x 120 bolt with nyloc nut missing for the drawbar hinge bolt.
Let's start building!