I thought about that too.
Right now, I believe Penske is selling 2006 or '07 SRW cubes, 12' by 80", but their GVWs are 8600 lbs. By the time you kit it out, it would weigh over 6500 lbs, so not much available payload. Hopefully soon, SRWs will be available @ 9600; if you're careful, you could...