OK, I got one of Mutazu's DMY trunks because it was the cheapest thing around and I only need to mount it on a detachable trunk mount and use it occasionally for trips. Had to drill a couple of new holes in my trunk mount, but got it mounted and put on the back rest.

Now I have 6 soft/thick rubber grommets/washers left over. There are 4 bottom mounting holes, so I figure it's not for them, but there are 6 bolts in the upper backrest.

I'm thinking these rubber grommets may be there to make the upper backrest more flexible so it won't crack the plastic, but I can't figure out if they go on the bolts inside the trunk, between the nut and plastic, or outside the trunk, between the backrest and plastic.

Anybody have any idea?

 

Those are called "Pocket Washers". When done with installation, any left over screws, washers, nuts, and bolts fit into this category.

On a serious note, some manufactures provide more than what your specific installation requires because it is easier and cheaper to include more than make brand/model specific parts bags.

Hope this helps.