Hi Carl,

Firstly yes you want to track the wan interface on the primary router so that it decrements hsrp priority enough for secondary to become active.

Secondly, on the secondary router I would just config a static route with high admin distance ie, 200, pointing to isdn dialer interface. So normally the remote site routes get installed into route table via igp from primary router, the static route wont take effect until these routes via igp are gone, because wan interface on primary has gone down, so now static to isdn is installed into route table on secondary router, and secondary router is also hsrp active, in order for other routers to route to remote site routes, you must also config to redistribute static route into igp on secondary.

HTH,

Cheers,

LR