You may be able to pick up a sail bag at a marine consignment store or a sail maker in your area Dede. It may be worth your while to buy a Mainsail cover and leave the Main on the boom all covered up.
I leave my O'Day 222 on a mooring behind our YC but years ago when I trailered my boat every weekend I used to leave my sail on the boom with the sail cover on it, tucked inside the cabin and ready to be attached to the mast after I raised it each time. I'd get the mast up and connect the topping lift to the back of the boom and lead it out of the cabin. It was like having an extra pair of hands to assist me in getting the boom out.
Back then, Davis was manufacturing a real neat sail jock which took the place of individual sail ties and it was always attached to the under side of the boom ready to spring into use. They quit making them years ago but I found a site that showed how to make one that works just as well that I'd like to share with you.
http://www.cncphotoalbum.com/doityourself/sailties/sailties.htm
My sails are getting pretty old now but they still have that stiffness because I try to keep them covered as much as possible when they're not in use and I always let the outhaul off when I cover them.
On these sail ties: I found that 3/16" bungee cord works great and instead of making them up with a hook at each end, I just omit the hooks and tie the bungees to the eye straps at each end of the boom. That way, if the bungee stretches and starts to sag under the boom, I can take the slack out of either side and re tie it.
I thought I had pictures of it in one of my picture albums but I think not.
http://forums.oday.sailboatowners.com/member.php?userid=78449&styleid=1 At any rate, I'll post them now for you.
Joe
