I used the same fix that chalowolf recommended. The water in my sump would fluctuate, if not from evap, then just plain old putting my arm in the tank. THE PAIN came from the fact that you carefully adjust the skimmer, then needed to reach in and do some work, the water would raise 1" in the sump, the skimmer would be overly adjusted for that period of time and for moments after, removing to much skimmate, overfilling the cup im minutes... or... worse yet, the evap after 1/2 day would drop the water to far, and the skimmer would not be effective.
I experimented with the location of the baffel between the skimmer and the return pump, creating a dam, high enough for the surge on the lower side not to rise above it, yet not so high that the skimmer wouldn't work...as there was a magical point where the higher water level assisted with the head to much, and the skimmer didn't work at all. (magical because your height will be different).
I Like the pail idea- its functional, yet, I am a little more fussy in that I would suggest a 2.5 gallon or 5 gallon aquarium set inside the sump. Theres nothing wrong with the pail, I just like to see whats going on everywhere at any time, in my sump. if it needed to be taller, I would get a clay brick or 2, (not concrete) and gently place them under the tank. Of course the skimmer and the return will need to be inside the tank, while the pump is in the sump proper.
The water top off... that's a tougher one...
J