UPDATE: Added varying severity of fillets (rounded edges/corners) for ease
There are a lot of custom D20 models out there, but I didn't see any where it was blank and available for customizing… so… I watched a tutorial on how to and have thusly made it available to you. If interested, the video I used from Youtube linked below (no assurances on video remaining available forever).
The author marked this model as their own original creation.