You should manually check the brakes as soon as you get moving down a straight, safe area, without anyone following you. OR you can just wait and see if they work the first time you need them! We check them after every hitch'up. Get up to 25+/- MPH, let off the gas, apply the manual brake lever. They should give a solid pull without locking up. After a while, you'll now what it should feel like with the lever applied 50% and won't need to go through a full braking yank. This doesn't take any time, unless you realize you didn't get the 7-way in all the way and need to stop.
You may need less boost on a rainy day.