I don't have any information to add to your how to list but I know that they are also using weighted coats (Thunder Shirts) for dogs terrified of thunder or riding in vehicles. Some of the dog sites may have information on stitching these that may also help you. I'm thinking that you would need to stitch individual bags filled with pellets and then slide them into channels in your quilt so that they can be removed if the weight needs to be changed. I sort of imagine that the filled bags would somewhat resemble the grain bags that I make (only longer) to fill with wheat to heat in the microwave. These are becoming quite popular so there must be some information out there somewhere. Good luck with this worthwhile project.