Many of us smoke sausage in many different ways than others do.
What works for one may not work for another.
So here is my take on using a water pan while smoking sausage in an electric, LPG or Charcoal.
My experience in sausage has been with a moist environment. True dry the casings for an hour or so to dry the surface of the casing. Smoke ad hears better to a semi dry to dry casing. Remember your smoked product will only take so much smoke, If your wanting smoke throughout the meat you may want to look at smoke powder additive such as AC Leggs or Spices Etc.
When I start the smoke cycle i use my water pan. The moisture helps keep the casing moist and from pulling away from the meat
(unless you have used protein lined casings) in which these will cling to the meat. The low heat will not boil the water, but keep a nice steady supply of warm steam. Larger sausage companies use soaked dust and/or warm water spray from the top down in a fine mist.
Experiment with or without water. Its your choice and all good.
Please post your water pan usage so we can all learn.