When I installed Interstate bags on my 81 Standard, I looked around quite a bit for an appropriate lid seal since the originals were pretty much shot. Not finding anything I liked in the traditional places (auto parts stores, McMaster, Whitney...) I got a little creative. I ended up using Larson replacement storm door sweeps -- the rubber things along the bottom edge of a storm door. Larson's part number is 2023197R. I got mine at Menards but any Larson dealer will have them. You will need 2 packages per bag as it's 38" long per package. Do not put the joints near corners like Honda did. Kind of center the joints at the ends of the bags or the ends will want to pull up.
The sweep is sort of U-shaped with the base being thicker rubber. This is the part that will seat against the lid. Remove the old seals and thoroughly clean off any glue residue. I used 7/8" wide 3M trim tape -- the good stuff they use to stick on car emblems. 3M Part number is 03615. Wrap it over the top edge of the bag so about half is inside and half on the outside. Sick that down really well and then lay the Larson piece over it and burnish it down really well. I cut out the "sweep" part on the inside corners so it would lay down nice and flat.
I did this 3 years ago and in 10,000 miles through plenty of rain I have never had so much as a drop of water inside the bags.
1981 GL 1100 Standard, 81 Interstate bags, 84 GL1200 pegs, sometime National Cycle PlexiStar windshield
1996 BMW R1100R
2007 Piaggio X9 Evo500, wife's ride so she can keep up with the GL
1980 Vespa P200 (also wife's), restored, with custom paint, custom trim