There is a thermocline in Superior. Only at the top layer are the temps 65-70. Three feet down its in the upper 30's.
I would ask David about camping at Rock island. They had a major storm last December. The lodge is fine but the beach is not. at least it was not in January. They are of course rebuilding.
I live half an hour from OOB. I would pay attention to what the natives do . Wetsuit. Every year or so someone takes a rec kayak out there wearing a bathing suit, gets washed out, cant get back to shore, flips,and dies of hypothermia.
Surface temps don't tell the whole tale. If you want one or two passes with the board you might be fine with no thermal protection. But a longer outing especially with wind needs a wetsuit. There are places to rent them.
2012 Honda Ridgeline
2016 195 RB.. 10,500 miles under tires as of today.
Been down many a dirt road in the west. We go where not too many rv'ers go.