I can't speak to your bumper of the applicability of mounting stuff to it. I know multiple people who put a multi-bike attachment on them and drug it down them down the road.. BUT, that's not what you're asking for.
I know that I've read of Herk (here on FRF) who built a generator platform and scrapped it after the first time he used it out of concern for movement... this is closer to what you're asking.
Here's what I do, though:
Plastic storage box that holds some sewer stuff (5' piece of hose, elbow, wye, and 2 x 50' expandable hoses that I use for black tank flushes). It's held on with zip ties. And, I can't imagine it weighs much more than a couple of pounds.