SIP Trunk DIDs to Google Voice accounts

I’m looking for a little provisioning advice.

Asterisk 11, FreePBX distro 5.211.65-1

I have some DID’s coming in on a SIP trunk and I want to forward each to a specific Google Voice account.

Apparently like thus:

exten => 100,1,Dial(Motif/google/[email protected],r)

I’m just wondering what machinations of motif/trunk/inbound route/outbound route/custom context/custom destination/custom extension/extensions_custom.conf… etc., would best address this?

There are other DIDs on other trunks and I really want to keep these DIDs as isolated from the main dial plan as possible.

Also, is this more of an Asterisk question that I should ask elsewhere?