I shall demonstrate why a 'gusset' that lands in the middle of a tube weakens the structure , not strengthens it.
So, in the 2 diagrams above we have a simplified cross section of the tow hitch.
In the top one, the 60x60x3mm Carrying tube is welded directly to the plate.
This is very very simplified
the entire tube flexes with load (every time it bounces) and 'pulls' to the right on the red weld. the weakest point there is the flat section just below the weld - smallest cross section with the highest load
thats 60mm x 3mm (or should be) and the tensile strength of mild steel is around 400N/mm^2 - so, that will take a load in the direction of load of 60x3x400 = 72 000N or 7,2 tons before it stretches and becomes thinner and brittle
In the lower one, there is a 5mm plate welded down the middle of the tube.
This causes the tube to flex only as far as the tip of the 'gusset' under load and redirects the force to down and right and into the unsupported centre of the tube where flex can occur.
effectively a good portion of the load is transferred to the point at the end of the gusset (the red weld) because it will flex there and not over the full length of the tube to the plate.
the weak point there is that the exposure to load is about 5mm x 3mm - or 5mmx3mmx400N/mm^2 = 6000N or 600kg before the steel is worked. less than 10% of the value of the fuel weld 50mm behind it.
Thats means the steel at that point will fail far sooner than the tube would have failed at had the 'gusset' not been installed
once there is a crack at that point, it flexes more and more easily, and continues to crack along the weak point (the end of the crack) until it gives up completely.
The idea of a structure is to spread the load into the structure, not direct it to a point load that cannot take the load!