I upgraded to 4g wire not for 55 amps of current, a lot of which the RV would be using anyway rather than sending to the battery, but to reduce voltage drop. My 8g wire would have had a significant voltage drop over that 15 or 20 foot span. (To figure the distance, you have to add the lengths of the positive AND the negative wire together.)
FWIW, I used the 55 amp converter for a few weeks with the 8g wire before I replaced it. I also left the 8g wire in place, just disconnected. If I ever have a need, in an emergency, I can disconnect the 4g wire and hook the 8g wire back up until a better solution can be effected. (I also still have the 45 amp circuit breaker I can reinsert.)
