Electric brakes

I agree with Fulltimer50 and don't envy your situation. Theoretically speaking each magnet draws 3-4 amps which is 36-48 watts and could create a fair amount of heat over time. However, the magnets would pull to the drum which would be a good heat sink to dissipate much of that heat. However, the RV industry is not known for robust engineering that would design a magnet to survive continuous duty cycle in this situation. I could be possible that the insulation of the wire would break down and short a winding. That could allow the magnet to function and give the appearance of working but not at full capacity. Therefore the brakes would work, but not as good as they should. A check of each magnet with a ohm and current meter and compare the readings to a known good magnet would provide more confidence. Also check the coil resistance to it metal house to make certain the coils are not shorted to ground.