Not sure if the rubber will hold up and remain in place, but is a great idea.
The SS belly pan is not worth the money if you're trying to save $$ use the 5052.
What I'm doing is using POR 15 on the mating edges of the bannana wrap the the frame then coat that edge again on the other side where it will meet the belly pan, when that edge will be painted.
The bottom line is that all contacting edges with be painted.
Also to reinstall the fiberglass is asking to redo all this work again. I suggest the the foil bubble R 14.5, it will not absorb water and sit there soaking and rusting everything like the fiberglass pink stuff.