That works. A few of us have made our own belts. I did one on page 4 of the 3D print build thread found here: https://www.whitearmor.net/forum/topic/49826-the-bigjasonis-rotk-3d-print-build-thread/page/4/ and @11b30b4 (Jeff) helped out with one on Kyle's build thread here: https://www.whitearmor.net/forum/topic/49604-r1tk-wip/. Since doing the 3d print build, I've learned a lot more about the armor and have made several updates, but the belt has remained relatively unchanged. However, I did switch out the ammo boxes for the far more accurate ones I posted in the 3D Print Repository: https://www.whitearmor.net/forum/topic/50811-rotk-ammo-boxes/?tab=comments#comment-715128
You're probably going in the right direction if this is what you're doing. The belt should be a fairly straight forward project, but it can also be extraordinarily frustrating. If you build your own belt, I highly encourage you to measure 10 times and cut once. In my build thread I outlined how I initially laid out the HIPS and cut my tabs, but then stated that "a flat piece of material measures different than a curved piece." I almost had to throw the belt away once I attempted to put it on over the abdomen. Get good measurements with the belt bent around your abdomen, then mark the tabs. Even my Jimi kit belt suffers from this a little bit. Not everyone is the same shape but the belts are pretty much made one size; when you put on your abdominal armor, then fit the belt, stuff stretches, or shrinks a little bit. This is especially true if your weight fluctuates.
Finally, I would encourage you not to try and make tabs that glue on top of the belt. You may get away with this initially, but the tabs snap off very easily. Gluing them back on is easy enough, but it really messes up the paint when you're repeatedly doing "field repairs." Also, since they're supposed to sit somewhat flush against the abdomen surface, you can't really back them with a second piece of ABS, otherwise they stick out too far and it skews the appearance a little bit.
Honestly, I'm starting to like the idea of a rubber belt.