>up tp like 250 a year can now be made by one manufacturer, don't have to pass safety standards
Build trucks. Pretty much all commercial trucks are 'custom'. Manufacturer builds cab and chassis. Aftermarket body and attachments added later. No standards that I can see. Hose reels, winches, equipment racks, etc. welded to front bumpers (often extended) pretty much with no pedestrian safety in mind.
How does all this differ from custom car coaches?
