Warm the polypropylene surface with a hair dryer or heat gun.
How to glue silicone foam mat.
Synthetic foam and silicone are good partners.
Applying glue to a small piece of foam place the two pieces of cushion foam that need to be glued on top of each other with the sides to be adhered facing outward as shown to the lower left.
To glue silicone rubber to metal.
Spray a solvent based activator accelerator aa on either the silicone rubber or metal.
Saturate the silicone rubber surface with an adhesion promoter designed to work with poly s.
Silicone can be glued but you often need a special surface activator chemical to prepare the silicone and the substrate to be bonded.
Bonding the foam together.
Silicone glue works best on silicone rubber.
People like permabond and loctite can do them.
Liberally apply adhesive coating both pieces and allow about 10 seconds for the glue to become tacky.
Rough the silicone rubber and the metal with a low grit coarse sand paper.
So yes you can use liquid nails type adhesives but you will be better off with their general construction adhesive than the milder stuff designed for polystyrene.
It is fairly easy to obtain at hardware or big box home improvement stores.