I very much liked other designs like this however my belt was 1.5mm and would not fit them. So I redid it and optimized the belt angles and curves to make it fit in smoothly while maintaining optimal tension and print without any anomalies. Works like a charm.
I've included the Fusion 360 file to import if you need to modify it for different needs.
You probably don't need 100% infill, but it's a small part with a lot of tension on it. It took me about 2 hours to print at these settings.
A higher resolution should allow the top chamfering to come through to allow the belt to slide in easily while remaining tight. I'd recommend running your print a little hotter than normal to maximize inter-layer bonding and there's no bridging to screw up.
When attaching the the second side of the belt, grip it with needle-nose pliers and pull it around the loop. While you want it plenty tight, if your carriage rails start sliding out of the side then you've made it way too tight and it will affect your Z-Axis in a terrible way.