the freezing was caused by the propane being drawn off faster than normal
its not going to hurt anything, but how long did it run
I imagine you only got a few hours out of that 20# cylinder
there are conversion kits for generators to convert from liquid to vapor, i have liquid LP onan 6.2KW,
some people convert their Onans to vapor
I think the main reason for the liquid feed, was too avoid the over chill and LP pressure drop on the tank, cause by running the Onan on vapor
this avoided problems with other LP appliances like the fridge etc..
this is my view, and i might be wrong