If you have a generator, the transfer switch would presumably also need to be replaced with a four-pole 50A transfer switch. (If you have to plug the shore power cord into a generator receptacle, that generator receptacle would have to be replaced.) Likewise, if you have a 30A EMS, you'd probably want to replace it with a 50A EMS.
Like some of the others, I would suggest replacing the 30A distribution panel entirely with a 50A panel, rather than making it a subpanel of a new 50A panel. The result would be cleaner and the work involved pretty nearly the same, I suspect. You don't need to replace the 12V distribution system or the converter.
This is a significant project, but not impossible for a DIY person who is knowledgable about AC wiring. If you aren't too knowledgable, seek out qualified assistance/instruction. Incorrect wiring is very often unsafe wiring.