Thanks to you both... You are right, @Bruce, it's right there in that link/document:   Default Route When configuring Hubs for a Spoke, there is an option to select a hub as being a Default route. If this option is selected, then that hub will be configured as a default route for the Spoke (0.0.0.0/0). Any traffic that is not sent to a configured VPN peer network, static route or local network will be sent to the default route   I checked that box, and outbound traffic is from Building A IP as desired.  Thanks again for helping out a novice! ... View more

I did see that, and perhaps read too much into "Blocked Splash page is static and is not customizable at this time" and assumed the article was outdated.   The reason I did is that the block splash page on an MX is in fact customizable as I mention, and the article does not address "Meraki hosted" vs. custom (self) hosted.   Still, I suspect the MX's Blocked page isn't customizable when the splash is custom hosted. At least, I can't figure it out but hoped someone here has.   ... View more