I freeze about the same way, the only diffrence is I go ahead and flour the sliced, clean mushrooms, lay them on a cookie sheet (no touching each other). When frozen, put them in freezer bags. When you want some after season ends, just take some out, pop them in the frying pan (no need to thaw) and they're just like fresh!
I do it exactly the same way, but I roll mine in flour before freezing on the cookie sheets and then transferring to freezer bags (burping out all the air I can). When I want some later I just put them in the hot butter right out of the freezer. Yum!!
my wife fries all of or shrooms then lays them out on wax paper to cool then puts them in freezer bags. when we want some we just take out what we want & put them in micro wave to reheat. taste like you just picked & cooked. DELICOUS!