Hello,
I could use some Velcro, or some screws (if I didn't mind the holes), or some sort of internal fasteners. But, for me the tape is great, because if I have to change a tire, I can just peel the tape off. In the winter, they have to come off anyway )slush and frozen gook would clog everything up faster than anything!
The tape is flush, it is quite effective, and all I have to to to remove the stickum is use a little Goof-Off and/or alchohol.
Coroplast is lightweight, easy to cut and fold, very durable, and cheap. (I paid $20 for the 4x8 sheet.) The hardest part (by far) was shaving off the back face and the ribs, so I could have the outer face form a flange that is nearly flush. I would make yours out of Coroplast to test their effectiveness, and then to use them as a pattern if you want to make them more permanent.
The line is where I had to bend the full sheet to get it into my car...