I have a assembly comprised of multiple parts, all of them being surfaces, and I am having trouble thickening them to run flow simulation. It is a car body, comprised of 7 pieces. I am able to add a center thickness of 0.032" to all of the parts, but when I do this I get errors saying that my surfaces overlap. Also, there are visible gaps in my model after I thicken it as well. Does anyone know what the problem could be? I can upload the model as well if anyone needs it, just suppress the parts not shown.