A question about tires on three axle fifth whl trailers.

I can tell you from pulling other things besides RV's down the road that you are not going to catch that rapid deflating tire by watching your mirrors, or by staring at the point where the tire meets the pavement.

Anyone pulling a heavy RV should invest in a TPMS. You can monitor all you tire pressures and temperatures constantly plus an alarm will immediately sound if there is a problem, prior to it causing damage.