Nice mesh and excellent choice of car! Those Jags are just beautiful.

Just had an idea looking at that mesh. You could 'fill-in' the perimeter of the interior to get a solid object, and then use Fusion 360 (free with an enthusiast license) to convert the mesh to T-Splines and then NURBS solids, then import those back into MOI. I've done that a few times from Blender and it's a fairly simple workflow. With a mesh resolution like your Jag has, it may produce too complex a solid.

Anyway, the object of the exercise would be to enable you to start the interior in MOI from actual NURBS intersections. That being said, with that workflow you're better off just getting the basic shape defined in Blender, converting to T-Splines, and using MOI to cutout areas like the taillights, but could be worth some research.