What an awesome idea! DH & I can no longer tow our TT for health reasons, so we have it permanently parked at a campground we love in the mountains. The only downside is that we can't camp at the local lake, which we also love.
I think I'm going to suggest this idea to my DH! I can see us getting a site on the lake at the COE and spend the whole day in the water. We could put up a small tent and a blow-up bed, so he'd have somewhere to lie down when DH gets tired. We could bring in picnic food and a cooler, so we wouldn't need to pack a camp stove. And who knows? maybe we'll just decide to spend the night, after all. :p