Free: Contests & Raffles.
Get hard sides and a spring lift for the drop tail gate. You can buy them or make them, just Google tail gate assist. I have a 5 X 10 looks like you photo and very happy with it.
http://seattle.craigslist.org/sno/fod/5476918282.htmlIf you're not driving an ATV or lawn mower in the back I don't think you want a ramp. Harder to empty as everything lands on the ramp, better to get a swing away or one that drops all the way down for offloading. http://ironeagletrailers.com/ironeagle/utility-trailers/voyager/
10-04 on the ATV, might compromise and use a separate ramp for the ATV? Like this. sure would be easier to offload garbage and gravel without a ramp in the way.