Custom aluminum diamond tread box. I shopped around and I couldn't even buy the metal for what this guy charged, and Northern Tool didn't have any size close to what I needed, and they were pretty high. This one was a little over $300 delivered to my front door. Clean welding, keyed T-Handle locks, it's really nice. It's basically a custon sized under truck box with the door opening out so it doesn't hit the back of the trailer.
The length will let it fit from just to the right of my power inlet to almost the end of the bumper. The height is 19", so that lets it not interfere with my taillight. Width, because of the way I'm going to mount it will probably stick out about as far as my spare tire, and it's large enough to hold my Craftsman Air Compressor, all of my plywood pad blocks, and some hoses and cords, all stuff that I needed to get out of the trailer.
My Outback came with a bike rack receiver that KS says is capable of supporting 200#, and that's with a receiver hitch leveraging on it. I'm going to mount the box on top of the bumper using 4" square U-bolts with plywood pads to distribute the load, so it will actiually be resting on the bumper. I think it's going to work out very well. If anyone is interested in having one made, PM me and I'll give you the contact information. If the Mods allow it, I can post it for all to see, but I won't do that until I know it's OK. I first saw this on modmyrv.com. The writeup led me to an expired ebay sellers page, but the guys contact information was on it and was still good so I called him.