Ramp and winch setup for 500lbs rolling weight?

Hi all,

I'm a new-to-me owner of a 2012 Prius v Two (though it has Softex, so unsure of the actual grade). A couple of times a week, I'll have to pick up and drop off a wheeled steel box that weighs 500lb max (more like 200 lbs in general). It has wheels and will fit in the hatch, but getting it up there will be the issue. Can anyone recommend a ramp and winch/pullzall etc setup that will work with the 12V plug back there? I'm a noob.

Thanks so much,

Allie