What you are trying to attempt is an unsupported feature on the ASA, bcoz ASA cannot do policy-based routing as in like a router, although you can try the document below and give it a short. But again, it is unsupported feature and might or might not work, but it is a workaround for it.
Thanks for the information and link. I completely misunderstood the dual-isp purpose on the ASA. The workaround looks interesting but if it is not supported I wonder how secure it is. Have you ever used it?
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...