You can upload a compressed folder for download. The compressed folder will act as a single file containing all of the car files. You can use different types of software, such as the built in Windows Zip, 7-Zip (what I preffer), or WinRar.
Here's the basics to compressing the folder and uploading here and will use the built in Windows Zip for you:
Make sure the folder you want to compress has the car files you want to upload.
From there, left click on the folder and go to 'Send to', then click on "Compressed (zipped) folder to compress the folder.
A compressed folder will appear below the original folder with all of its content. From there, you can upload the compressed folder here for download without a problem.