This is what I bought for storage. It's a 48 gl. Rubbermaid Action Packer. It fit surprisingly well. I cut slots in the bottom on each side for the loops for the seat mount to fit thru and then installed flat mounting plates under each loop and screwed them to the bottom. Sorry I don't have a photo of that part. It sits flat and doesn't rattle or jump around at all. Not sure if this is what you want, but maybe it will give you some ideas.