You can also dry them in a very low oven. But it takes hours, so not very economical unless you have lots. (Or an Aga!)
We had a monster haul of ceps a few years back and I think I've got enough stored away in jars to last the rest of my life! Just one or two slices added to a casserole reals lifts it.
Another way is to make duxelles: dice them finely, with some garlic & onion and fry the whole lot very slowly, stirring frequently, until all the moisture is evaporated. Again, it takes an age. But the result can be frozen in small quantities, to be added to casseroles, etc as you need.
You can freeze the soup, of course.
You must have had a lot more rain than we have here. Haven't seen a single mushroom yet and we're well into the season.