Okay, so I want a Routemaster because I want a unique style Motorhome and I have found very few Routemaster conversions (Probably because of the concerns that people have made above).
I have found minibusses or vans are a bit small, I like my space, so I thought about getting a vintage American A class Motorhome because that would be unique and cool, but unfortunately, LHD vehicles are not allowed to be imported to my country, so that is not going to work.
Compared to the UK my country is quite liberal with size limits, as for the costs of running they will still be high but 1. I don't have other major expenses (Except model trains) and 2. I feel it is worth it for something as cool as a vintage bus. Also, vintage passenger vehicles are a lot easier to import into my country as long as they're over 40 years old. I know Britain does have some Small RHD motorhomes but for the price of them, I would rather buy a Routemaster. As for the conversion cost I view this as a long term project.