If anyone else is struggling with this one I’ve at last been able to fix my Grand Caravan livery by amending the texture.cfg as follows:
fallback.1=…\texture\Livery
fallback.2=…\texture\AS1000
fallback.3=…\texture\Gauges
fallback.4=…\texture\AS700
fallback.5=…\texture
fallback.6=…\texture\AS140
fallback.7=…\texture\Extinguisher
fallback.8=…\texture\Lights
fallback.9=…\texture\Glass
fallback.10=…\texture\DetailMap
fallback.11=…\Asobo_208B_GRAND_CARAVAN_EX\Texture
fallback.12=…\texture\Planes_Generic