Great idea jsm and presented in an original and arresting way, unfortunately it won't work long term due to the leverage on the swiveling arm.This arm will fatigue and break in transit due to the weight of water, if it was stronger, or had a brace it would fare better.
My prediction is it will bend, drooping the reel down at first, and eventually sheer. If you can find some way of offering it a bit of support when the van doors are closed it will last better.The load bearing while you are actually working is fine.
As for a name, something short and snappy, i think it should be called a john malone catherine wheel.(less snappy).