I think that I would enjoy tubing year-round and on the sand dunes near Ludington I can do just that. Not with a sled mind you but rather a saucer. Metal saucers would move well even on dry sand and whiz you down whatever sand dune you choose faster than a speeding bullet. As on snow, sand serves as an excellent feeding system to a saucer.
There is a caution to be raised however in that I would suggest that if you go tubing in the summer time that you choose a dune not to close to Lake Michigan. This is especially so on those large dunes that almost runs into the lake. Can you imagine hitting high speeds down a dune and then go flying into Lake Michigan? You would almost be like one of those stones that kids toss into the lake to make it skip. You could bounce out quite a ways and then have a hard time getting back into shore.
I prefer using saucers on dunes that do not run directly into Lake Michigan and I can have just as much fun on those as anywhere else. The only drawback to saucering down sand dunes is that you have to walk back up them to do it again. Maybe some day someone will install a saucer lift like those ski lifts? Nah!