Shouldn’t be too much of an issue. Is it possible for you to convert the entire body into a single piece? The wheel can stay separate. Do ensure that the faces are solid as well as if they aren’t, it might cause issues.
I’m currently meshing your geometry. Will get back to you on it when I’ve found something.
EDIT: I’ve uploaded your geometry to OnShape and there are some serious errors. It likely has to with the surface not being an actual surface and just a bunch of data points hence the errors. Refer to the screenshot below.
So the meshing settings is not the issue and its the geometry. You need to go back to the source file and ensure that the body is solid and export it again. Maybe try a different format like IGES to see if might alleviate some of the issues.