Here is a pic of the underside - as you can see, the generator and the battery box are not any lower than the axle:
What I'd be concern on rough roads is bounce. It that became a problem, this setup looks to be a good candidate to replace the bump stops with a set of timbrens. Looks also you could easily raise the rear end a couple inches without extreme measures. But I doubt any of this is really necessary if you take it slow and easy.
In fact, I've found the stock setup to be such a smooth rider that my bins and gear in back stay put and the contents of my cabinets stay in place too.
