RV furnaces are like
lights " their either on or their off" . The furnace is designed for a fixed BTU imput and output. You cannot vary the heat output like you can the speed of a car.
If you desire more heat just turn the thermostat up and the furnace will run longer before it satisfies the thermostat. Turning up the thermostat to 90 deg will not change the rate in which your trailer heats up
As far as the pilot flame not staying lit , it could be a multiple of things.
IE : Incorrectly positioned thermocouple , bad pilot valve , pilot flame improperly adjusted , high or low gas pressure , bad gas regulator , corroded thermocouple , a backdrop blowing out the pilot flame , ETC ETC.