So the biggest problem with the rv-series when it comes to site-to-site vpn is that the local IP address in the profiles must also match the IP address of the other side when it tries to connect. In other words, you have to have the public IP address in the router on both sides. You can't get this any other way other than disabling the router built into the Comcast modem/routers. (There might be a way if you have NAT Traversal as an option on the rv042, but I've never had any real success with this.)
Once you disable the Comcast routers built into the modems, the routers will get the true public IP address and should connect instantly.
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