Would a slight toe-in on jet tip tanks track better in the air ?

Don't see it, its just going to add tip drag and possibly give you adverse (opposite) yaw

It is toe out on some full size aircrafts, the most noticeable being the F18F, but on a model I would just leave them at 0°.
However you can put them at a slight down angle, maybe 1° this will compensate the shift of the center of push.

The super hornet is angled out for separation issues (ie dropping or punching stuff off so it doesn’t come back and bump into you). So not necessary for a model

The down angle of tanks on the FS is so they are aligned with the relative wind for normal flight (ie compensate for angle of attack). Makes sense in a model for lowest drag. For tip tanks I would think same incidence as the wing but there are smarter people here

hope it helps!

Thanks for the help guys.
So if I understand correctly, for a model, the wing tip tanks should be parallel to each other and same incidence as the horiz stab (which has 0* incidence in flight). Right ?

I think the same incidence as the wing, but there are smarter people out there. Yes parallel

Dave