I tend to just fill the SR4 with hot water and leave the valves open a crack...
On a serious note though, I have considered the same thing, but never got round to implementing anything. Given how much it rains up my way, a bit of shelter when fishing/camping would be great. I am not talking luxurious galley cabins like the big ribs, but something ruff and ready as it would have to be light, and removable. My main ideas where:
SR4 Deluxe - add side and roof to windshield back and up about a foot or so to give some extra rain/spray protection.
Or remove bow dodger and attach small fibreglass/wood cuddy to nose area in its place. Could sit on tubes attached to top strip. A couple of feet high would give enough to duck out of rain and keep the bow fairly dry. Could put a small windshield on top if jockey is used.
Or make a new, bigger, detachable bow-dodger that is high enough to duck under out of rain or even extended further back for more camping shelter. Or reduced/removed/replaced for speed/fun boating.
All untried of course , but food for thought. Do post pics if you come up with something!!