Hope this idea helps somebody else!

When I bought my Heritage in 99, I remember looking at all the sagging bags on similar bikes that were only a few years old. So the first thing I did when I got it home was build a wire frame for each bag and now after 14 years and 95000 miles the bags still are holding their shape. However, after all those years of rain and sun, the tops were so warped that they wouldn't even keep the rain out anymore. I wanted to share what I just tried that worked really well for me.

First I laid the bags out on the floor, and blocked, clamped, and weighted them until they were in a more proper position. I then heated several cups of water in the microwave and thoroughly soaked the entire tops. I have now let them dry for a day and a half (couldn't wait any longer) and put them back on the bike. Night and day difference!