John, have you seen mine or Damiens? Come and have a look sometime, both are good designs. Mine weighed 440kg without the ramps. (probably 15kg each)
It's somewhere in between the one pictued above and 900 kg Titanic hire spec trailer.
It's all duragal so you only paint the welds, has a 75x50x2 drawbar with a 50x25x2 triangulation from the hitch to the top tie down rail to add strength without going massive on the drawbar. Full tandem axle load sharing springs, 15" Light truck tyres on 2WD Hilux rims. Removable Winch, LED lights etc.
Override disc brakes on the front axle and a drop tail so low cars load easily on 1200mm ramps.

Damiens is similar but not a drop back, it's a break back instead. He uses his for building materials as well so wanted a flat floor. It's a bit bigger and a bit heavier.

Both trailers tow superbly and are evolutions of a proven design.

Edit; I don't dig aluminium car trailers. Aluminuim boat trailers are ok, but car trailers need too much welding and potential for fatigue is greater. A friend biult one, it was heavier than mine and the drawbar eventually broke off it.