Re: Storing the mail sail
With my load-path mainsail, I DO leave it on the boom (under cover - waterproof top, open bottom)... I had a discussion with the sailmaker over it, the discussion was that basically if I continue to roll the sail and it not get put away wet for long periods, that it should hold up as well as rolling and storing in the original sail bag, in a dry place. The critical part is do not fold it! (again this is a non-issue with dacron).
If you are really thorough, you'd store rolled, stuffed in a bag, rolled, not-folded, and in a dry cool place (is why you see racers arrive at the marina with their sails, having to bend them on EACH time), if you have a racing set and a practice set, this is probably the way you want to go.
Paul's technique has been one I've had a tough time replicating (might be the smaller size of my boat)... but I just roll head down, until I get to the boom. I leave battens in, making sure they stay parallel with the boom all the while rolling. The only interesting part of this is the loose foot main makes the whole shebang flop on the boom (until I get it tied off). But I've been doing this for 2 years now, and it seems to work fine.
I agree with the sailmaker though if it gets wet, you can see how it could super-heat the sail when the sun comes out.... so I get back as soon as it's dry and air out the sail.
I have a load path 155 genoa as well, it gets dragged up to dry land after each use, rolled (also top down cause single handed it's easier than bottom up, and rolls tighter), then gets stored on my boat (as its pretty dry on my boat). It rarely gets above 85 degrees at my boat (I know much hotter below), but I also have shade (yup) after about 4pm at my boat, so it cools off quickly there.
As for dacron. I'd leave it on the boom, flake it.
Just a quick look and it sounds like you have a J/22. Getting practice dacron sails might be a huge help for you, them you can leave on for practice sessions, and just change sails to the load path stuff when you race.
I only have 1 functional mainsail (my loadpath), my old dacron sail has seen better days. I DO however, have a functional 155 dacron, and when I am just messing around, it's the sail I pull... I also have a 130 which is JUNK (no leech line), but it works as the winds come up. The 130 is usable for me up to about 20 knots. After 20 knots I am reefing my main, at about 25, I am reefing my main, and also using reef knots in my 130 (yep it looks like heck, but I can do it, and it's designed for that).
As far as dacron stuffing versus folding? Stuffing is a must get rid of the sail now, thunderstorm coming, kind of thing. Folding is the ONLY way to properly store the dacron sail tough, and YES it takes up less space, but also it doesn't look like a shirt left on the floor overnight before being worn.
J/22 is a fun/fast boat, enjoy it.
Hull #68 S2 7.9 on our little landlocked puddle, Lake Wallenpaupack, PA.