I'd wager it's somewhere between zero and 2000psi....
Seriously, master cylinder piston size, pedal lever ratio and pucker factor, per Ironflight, all factor into the brake system pressure.
An example would be for a 5/8" piston with a 3:1 pedal leverage and a 200lb man (100 lb per pedal) lifting himself out of the seat. This equates to aproximately 1000 psi. I don't have the dimensions for an RV at hand, so YMMV