The kind of hybrid surface I park my enclosed trailer on is functional, well drained and works. It was a good bit of manual labor though. I did have the disadvantage of needed to dig out about 3cy of soil to create the relatively flat spot for the trailer spot near my shed in the backyard. That was one very sore Sunday digging all that out by hand. If I ever do something like that again, "rent-a-hoe" here I come. I did the passing though on pouring concrete, but ready-mix ain't cheap, and trying to float something 12' wide with limited help was too ambititous even for me.
So what I did was a mix of stone and pavers. The subbase of the parking spot is 6" of quarry process/DGA, and from a patio/basketball hoop project going on at the same time, I used the leftover 12"x12" concrete pavers to create a pair of 2' wide "runners" for the trailer tires to sit on. Another couple pavers are placed near where the tongue jack comes down for a solid surface there. Since road base stone is ugly gray and will grow weeds better than potting soil, for surfacing I got a delivery of landscaping stone, with what I picked out a lava rock that is a dark red, tan and brown that goes well with the house and shed siding, the red patio pavers, backyard fence and landscaping. The space has about a 2.5% grade back to front. It never ever has water standing, as the landscape stone has a lot of voids and the DGA is well drained. I have this same surfacing section on the entire path I drive the trailer on to get it from the driveway to the parkign spot, and it has held up really well since I got it all finished in 2005. The trailer is going on 6 years old and the steel frame underneath looks great.
Materials all-in to do this for one spot would be under $500 delvered.
(on edit - added a picture of the finished job)