Wet brakes in or out........
True about band brakes getting wet and fading out. My last project, a minibike, I wanted to avoid that so I went with internal expanding shoes drum brakes, harder to get wet, and still work better than bands when they do. Didn't have the option of a whole lot of cable pull due to the use of a handlebar mounted brake lever, but a kart can get a much greater amount of pull action by proper attachment to the brake pedal.
My brake shoes were dragging in the drum because apparently no drums come perfectly round, or it's that bearings don't come perfectly straight in wheels. Point being I had to adjust them that close to get any real braking with a full pull of the lever, and even then couldn't lock the wheel up. You use those on a kart and you can adjust loose enough not to drag even before being broken in (like mine did) and still get enough pull to lock the tires. All mechanical, very strong grab, hard to get wet, makes for very reliable braking, that being the most important thing.
NOTE: I'm talking about using that setup on a live axle where both rear wheels will brake, not a single wheel brake, that's dangerous.