I'm with Joebloggs re putting the straps under the seat (keeps them on, but also saves the seat cover from damage).
I'd just be wary of the masking tape though - the glue can mark plastics when left in place for a while, and it turns to mush if it gets soaked - there are clear plastic films that you can get to cover panel areas you want protecting and I'd use some of that.
[size=78%]Panniers look like a bargain though 😀[/size]