It would have to be created, since there's no public model for a HeaterMeter 4.2 case that doesn't have USB / Ethernet ports on the side. It could probably be created somewhat easily by taking Tom's design and just removing all the holes though.
I've used Fusion 360 to make changes to the case before. It is a pretty popular bit of software for doing 3D printing modeling and it is incredibly powerful since it is a professional-grade product. A license to use it is free as long as you promise that you're a hobbyist and won't use it at a company that has more than $100,000 in yearly revenue. Autodesk has their own people who put out tutorials, but since it is used by so many hobbyists, there are a lot of third party tutorials on youtube as well. The only drawback is that they have drastically improved the product over the past 3 or 4 years so a lot of the functions in the UI have been reorganized or renamed.
I'd take a stab at making the case you want but I don't have it installed on my computer currently.