AHi, I am quite experienced in cake dec but I'm in disparate need of a good recipe to crumb coat a cake. I need to ensure that it is as sturdy as possible as using it for a car cake Any help would be much appreciated

You can use any buttercream recipe for the crumb coat, use whatever recipe you normally use.  You may want to make add a little extra liquid, milk water whatever, so it is soft enough to not tear at the cake.  All the crumb coat does is seal in the crumbs with a very light layer of icing, it doesn't add any structure or sturdiness.