One option you can try is 3M™ Double Coated Tape 9490LE. This tape has 3M 300MP adhesive on the faceside and 3M 300LSE adhesive on the backside (liner side). 300MP adhesive is extra conformable and designed for foam bonding, so the faceside would go on the foam. The backside 300LSE is designed for low surface energy (LSE) substrates, so that would go on the santoprene. Please comment below if you have additional questions or would like to talk about other potential options.