Hi Stu,
I had a similar idea about geting a generator to run my Henry for car valeting. However due to the large current drain by the Henry's motor on start up, I apparently needed to buy a generator with something like a 2.2 Kva output. These are quite large and I don't have enough, (any) space in my van already so I left it.
I'll be interested to see what other replies you get in case there are other options.
Les