I found a solution on the Reddit forums that works for me.
First setup your tailscale remote subnet router on the Mt3000 as usual. Then…
On the MT3000 Admin Panel
Under menu item System->Advanced
Go into the LUCI admin panel then select Network → Firewall.
By default, below you will see 3 zones:
- lan > wan
- wan > REJECT
- guest > wan
Click on “EDIT” on the second one ( wan > REJECT)
Then click on the second top tab “Advanced Settings” and in the covered devices dropdown select tailscale0. Save, Save and apply.
Now you should be able to route your Mt3000 Wan traffic to the designated Tailscale exit node, and the devices on the MT3000 Lan will also be accessible to devices running on the Tailscale net
One slight bug. On the wan side you will not be able to reach the admin console of the MT3000 via tailscale even though it is included in the subnet routing address you setup And you will not be able to access the admin console of the MT3000 on the lan side unless you turn off Tailscale on your local lan device, which is fine since all traffic on the lan side is now going over the tailscale net to the exit node anyway.