ReproBox3D is a web based tool for previewing your retro game box designs on a 3D box.
- Download one of the supplied templates
- Open the template in Illustrator and create/apply your design
- Click File->Save for web...
- Select PNG-24 and Uncheck "Clip to Artboard"
- Change width to 2000px
- Press save and upload in this tool
- NES cart: PNG file 500x879px