I forgot exactly where I got it, but it is the same as this one: http://www.deiequipment.com/armor-rex-motorcycle-rail-kit-745-746-749-trailer-kits-black.html?gclid=CImbwsmskbUCFVCd4AodSF8A9g
It is an adjustable rail (in length) with a ramp rail and ramp rail mounting kit. The mounting kit allows you to store the ramp rail underneath the trailer. It fits my 160 rear no issue and it should fit 180 either, but not sure about 190.
To be honest, IF you have a vehicle that can tow, I would absolutely suggest you to get a 4x8 WITH a ramp gate, similar to something they sell at lowes site, but it will be a bit more expensive.