I bought a second hand 4sq.m storm jib by Quantum. It has a sleeve to go over the furled genoa, with piston hanks to go through the rings on the sleeve. I have never used it in anger, only for practise. It tacks down to the mooring cleat just aft of the roller curler drum. Seems as effective as I could hope it to be.
Hope that's some use.
Dick
Dark Star P275 No 36