I bought a 48 in. square waterproof patio table cover that just came in yesterday.  Just today I did the fitting well enough to cover Surprises whole cockpit, with a good sitting room under the beige cover that covers the whole open area.  One detail is I couldn't cut the existing bimini top bows enough to do a deck level fit.  The other side of that is there will be some air flow under the cover for circulation, and I don't camp on board now anyhow. 

Maybe it beats heck out of carrying a full boat cover, and might be able to be added on under way for spring showers.  Just flip it over the bimini to install, and wrap a couple corner knots.  Maybe I can add  an entry hatch later as time permits, or I can get somebody to do a bit of sewing.  I put in eyelets to snug the corners tightly, and the color matches the afterdeck oak pretty well, oh yeah -- the table cover was $46.00 with freight through amazon, nylon cord and some grommets extra. 

Sure helps to have a bimini top in place, but with some thought, a  simple bolted and removable 2X2 frame could be added to fit, and sized to fit the basic yard tool box, BBQ fire pit, or like mine a table square cover for a weatherproof cover on the cheap. 

Gettin' er done to see if I need more detailing, byeee !! -----  Cal