Hi Tim

So,if all problems are related to render your vehicle,you should post your questions not here,in a modeling forum
my suggestion is always model in real scale from the beginning
when you export to a render platform,you need to have camera,distance from object all in coherent scale
As you can see it's just 128 millimeters,check in your Blender scene if all is in scale
It's a toy model or a real vehicle?
Dimensions in millimeters



I suggest you to get a solid without mirroring
Avoid patches like these




I did something like that in the past









M