Just FYI, I tried a nice mainsail from West Marine with the adjustable panel to allow it to fit a 1- -12 foot boom. ITS A NICE, WELL CONSTRUCTED COVER, BUT, IT DOES NOT FIT AROUND THE MAST.
The mast diameter is just too big, and you cannot close it up.
Looks like I'll have to either make my own with a Sailrite kit, or, take some measurements and have one made.
Chet