On these guys:
"These guys are water-cooled serious:
https://www.youtube.com/watch?v=hXfod6pgymc"
There's hum. Is that from inadequate filtering? I see or rather hear that a lot on the few 'big' stations in my area. The youtube videos of 'amp builders' sometimes show just a bridge and a single oil cap that can't possibly have enough uF to filter the HV as well as a regular ham radio amplifier in that department.
There's a video out there of 'Prime Minister's' workshop. It's very nice, orderly, and little expense has been spared. There are large machines there that are of the fine quality that might be found in a small electronics manufacturing company and so he can build up most anything he wants from panel to plug. The place has more square FT than a small house. I could not find that video just now but it's well worth watching if it pops up.
As far as a mobile, I am in the market for a hearse myself, and perfer a 'full size' GM product with a 455-500 cube motor of 1971 spec or elder. Torque! Not too concerned about some rust or appearance. up to a point.