I have thought about making a tight-fitting cover for the dinghy, ... with a ridgepole (probably mast) stem to stern underneath, It should keep water out. Anyone try that?
I did a sunbrella tight fitting cover for a RIB dinghy, the bungees were tight enough the first year to support the cover and keep any water from accumulating, but the second year the bungees needed replacing. So i put up a collapsible pole, BoatersWorld. The only difficulty I had was the bungees attaching just below the dinghy rub rail, otherwise the bungees would have run underneath the hull and there add minimal drag, but accumulate growth.