How to make a car 3D printable?

Hello! I have a STL file of a car body (1 and 2 photos) and want to remove the windows, the floor and to add some thickness to the panels in order to make it 3D printable like on the third photo. Polygon count is 33000 which is too high for CAD programs, also it cant be converted into T-splines. Which program should i use and how to do that? I would be very thankfull for the help!

Accepted answer

Check this. I scaled it to 150mm and made a 2mm thickness. Is this what you want?

1 Other answer

here is the file