Basecamp to make GPS guided routes

I'm new to Basecamp and have started to plan walks via the map base (Garmin v4).
It seems that walking tracks are not routable on the v4 and as such I need to manually create tracks through non-routable sections. Bit clumsy but thats OK. Question is - how do you create a walk that combines routable sections and manually created tracks (non routable sections). I expect to be able to just join up the different segments but Basecamp doesn't seem to allow this - any advice?
It seems that walking tracks are not routable on the v4 and as such I need to manually create tracks through non-routable sections. Bit clumsy but thats OK. Question is - how do you create a walk that combines routable sections and manually created tracks (non routable sections). I expect to be able to just join up the different segments but Basecamp doesn't seem to allow this - any advice?