I have been reading quite a lot of posts concerning saggy bags especially on the Heritage and have been shocked at the prices charged by company's who address this problem.
I took mine off recently and made paper templates of the insides of the lids and a mate has made 2 PVC inserts 3mm thick to go into the lids from some scrap materials. I managed to get a tin of Industrial contact adhesive for £5 ($10) and glued them in and left them over night to fully cure.
The bags look great now all for £5 and I will take some pictures later and post them here
You should go into buisness for yourself with the parts you made, and sell them for $30 bucks, or what every currency you use less than the next best thing. You can make a fortune.