Sounds like you may have overcome the meshing challenges, however if I can add a comment, in the case the point has not been explicitly made yet. In SW (and CAD in general) you want to keep the geometry as a solid at all times, and for external Aero, you want to get it down to a single body, and then remove that body from the “air box”. Remember, we are solving for fluid flow, so we really want to mesh the volume outside of the vehicle, not the inside.
To get a single body for the FSAE car in SW, save the assembly as a part file, this will produce a “multi-body” part. Open the part up in SW, and then consolidate to a single body part using a series of Boolean features (rarely is the geometry clean enough to just use a single combine feature). If, at some point, you end up with a mix of surfaces and solids, then there is a “cut with surface” feature that @oscarcorripio mentioned, but for it to work well, then geometry must meet certain criteria. Once you have a single volume representing your vehicle, then import it into Simscale using a *.stp file format.
When using this process, any troubles with consolidating the assembly to a part can easily be addressed within the CAD tool, and typically it is due to sliver volumes, small gaps, and point contact between parts where the cross section becomes zero. These issues will cause you meshing errors whether it is a part or an assembly, but when it is brought in as a single part, the file size is smaller as well. I hope this helps.