Only two things I know of that will limit the number of burners you CAN use.
First is the size of the regulator at the tanks and second is the amount of heat you can stand in the RV.
At one time during a family outing I had all three burners on (at different flame levels) as well as the two burners at my outside Kitchen running. With all windows and vents wide open it got a little warm inside.
FWIW, I dumped the tiny, cheap, regulator that came on my trailer for a Marshall MEGR-253 regulator that can deliver 225,000 BTU/Hr. Old one was about half that.
