With the tower... all you can do is, to have a custom cover made with snaps. (Like a morning cover) I have seen a few custom covers that have an open section, that will Velcro closed, and that allows you to close the cover around the tower. Regardless... it's not going to be a "Towable" cover.
Poppy covers have a large ratchet strap in the edge, and that allows you to pull it tight. But... that strap can't be there since you would need holes.