We previously had two Californias which we hired for a couple of years to cover the running costs. Generally went well and very busy as were lived in Kent and plenty of demand to take them abroad.
If ts not your day job then don't underestimate the work involved or the time needed to prep and hand over. Also be very careful of back to back bookings as any issues or damage when the van comes back in will be difficult to sort in time. It can be pretty stressful, we had our blue one driven into a raised central reservation, one reversed into a tree breaking a window, one ripped bellows and another returned with a shredded tyre!! The excess covers this but its pretty heartbreaking when its your own van rather than just an asset used in the business. Also, depending on the insurance there is likely to be a hefty excess and some difficult conversations with customers. And don't forget the calls about how to lower the roof, find the gas etc.
I'd be very wary about the insurance if going through broker and where your own public liability lies in the event of a mechanical defect causing an accident. Keeping detailed maintenance records is very important. Also will need to register as self employed, complete a tax return and possible pay NI (class 2 and 4) depending on your profit although a lot of expenses can be offset - you ned to factor in accountants fees and also making are you have a watertight hire contract.
For us at the time it was the best way to have a Cali for our own use economically, but we wouldn't do it again. Not saying its impossible, but go into it with your eyes open.