As I understand it, the cushion base only needs the two holes at the back for the belts. The cushion back doesn’t require any holes, but some family members are using the vertical holes for chest straps. I’ve made the following modifications in Fusion.
Does this look right from an only necessary holes design perspective?
Looks good to me. I will point out though, the bottom 2 holes in the bottom cushion are there for a center strap and some families have requested that. There is a part to have it work with the lap strap on the google drive.
So the only unnecessary holes are the 4 top holes in the back cushion?
I guess so. It lines up with the top “medium” straps but in the instructions and the build guide video they don’t put the straps though those holes.
If your having issues with the horizontal holes on the seat bottom I just uploaded spacers to insert for bridging. It helped a ton and they look great.
https://makerworld.com/en/models/2907467-tmt-tpu-cushion-bridging-spacers?appSharePlatform=copy
I just finished my second seat bottom using them. This is before any cleanup.
My “Feeling” about the holes in the Top Back cushion is that they aren’t needed. I couldn’t print the top cushion at all, nothing but problems. I have six, seven of them that I now use for kneeling pads…lol. If someone needed to use one of those holes, a razor blade would be what I’d use to slide the belt through the cushion. The cushions are not airtight, so that wouldn’t affect the integrity of the cushion. I also think the holes make the cushions less soft in those areas. My OPINION and it is just an opinion.
Those spacers look like they work great.
No problems personally. I was editing the back and I figured I’d provide an additional option.
I put the straps though those holes on all my builds. 
That is what I was going to do on my first build until I watched the video build a few times and saw that they were actually going behind the cushion.
I don’t think it maters either way.
I honestly dont think it matters either way 
