my 24 foot Grumman pontoon boat is on a lake that will be drained for 6 months. Is it OK to let it just sit on the soft, muddy bottom, which of course will dry out?
no if it was mine i wouldn't, if you don't have a trailer for it i would borrow one and get it out and if nothing else get some old tires and set it down on them, leaving it set in the mud will cause corrosion on the pontoons, better yet just pay someone to haul it to your house assuming you don't live right on the lake.
They set them on styrofoam blocks or tires around here for storage in the winter. I do think it would be a good idea to get something under them. Put several under each toon to disperse the weight/stress.