I have seen some seat belt work here and thought I'd give my method. I use that aluminum dead-soft duct tape, cut it into appropriately sized strips and fold the strips back onto themselves adhesive sides together. Because it is aluminum it retains any conformity desired and double-backed onto itself gives a suitable scale thickness. It is also good for making faux panels on airframes and is superb for adding fastener detail too. The adhesive is pretty aggressive and, again, being aluminum is can be burnished into compound curves using a little finesse. Food for thought.