Best choice for gap filling?

I'm looking to fill about 1/16th to 1/8th width, 1/16th depth on the 53 ford crestline's trim belt, in order to build a mild custom without the trim. What's your best filler choice in this case? (I have tamiya putty)

Ideally strip styrene or just glue the provided mouldings in and sand off the excess.

Kurzheck