Ubuntu Policy-based Routing Issue

This is an extension of a post I made last week: https://www.reddit.com/r/networking/comments/k6rw80/bgp_ospf_route_redistribution/

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Updated Topology map: https://imgur.com/F8ls1ii

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Recap: I'm trying to route public "reserved" floating IPs from Vultr (RT1/2 are peering with Vultr) to RT3/RT4 (on-prem) so that I can use them for hosting services on-prem, The ZT transport is occurring over two internet connections (cable + LTE backup) for failover.

Here is where I stand so far:

1. RT1 and RT2 are correctly advertising BGP routes to the 45.63.78.104/32 loopback on RT1/RT2 and 104.207.141.245/32 loopback on RT2/RT3.
2. If I ping 45.63.78.104 from the outside, I do get replies.
3. If I ping 104.207.141.245 from the outside, I do not get replies. When I tcpdump on RT1/RT2, I can see traffic being received on this address. When I tcpdump on RT2/RT3, I can also see traffic being received on this address. (I needed to disable reverse path filtering to make this work). However, I'm still not getting replies. I'm pretty sure this is because the reply is trying to leave the default gateway on RT2/RT3 which is NOT RT1/RT2...

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What I think I need:

1. I need policy-based routing so that traffic received from on the ZT interface is not routed out the default gateway on RT3/4...I need this traffic to go back up to RT1/RT2.
2. I think I would also need to use VRRP to establish a floating IP between RT1 and RT2 that RT3/4 can use as the default gateway for this policy-based route.