Im using this type

I dont want to go down the rubber strip type to hide the pop rivets as I dont fancy having the rubber showing on the outside.
Ill be using 3mm alu bar on the inside. Therefore can you get a rubber seal that will hide the ugly side of the pop rivets?
Crude diagram attached!

Above im trying to show a rubber seal idea, the trough in the middle would hide the pop rivet heads?
Any help or better suggestions would be great!