Our expectation is that it should be correct -- but it looks like it wasn't for you! The anomaly should probably be reported as a bug.

Simming them is straightforward. Looking at a design report it seems like creating drill templates with holes for the motor mount tubes is also straightforward, but the various mounting holes takes some finagling.

For simming, just put a centering ring at the back end of the rocket. OR assumes the back end of the rocket is closed, so you get the right base drag without any extra work. If you're concerned about different surface texture causing a problem, put a short length of body tube with the texture you're looking for.

I think (without trying it) that you can put a cluster of inner tubes at the right places in the thrust plate and it'll put holes in the drill template. I haven't worked enough with the .obj export to know if it'll put the holes you need in that, but I'd expect it to.

This is the first I think I've ever heard of people building rockets with no aft centering ring.

I wouldn't say that a thrust plate replaces an aft centering ring, they are often mounted to the aft centering ring. but they sit externally to the rocket instead of internally. Some, namely the ones machined from materials like aluminum, may actually incorporate the aft centering ring as a single piece of material.

It's the statement that the thrust ring plate keeps dirt from getting up in the body tube that surprised me.

It's the statement that the thrust ring keeps dirt from getting up in the body tube that surprised me.

I don't know who said Thrust Ring... I know I was talking about Thrust Plates.

It's the statement that the thrust ring keeps dirt from getting up in the body tube that surprised me.

I don't know who said Thrust Ring... I know I was talking about Thrust Plates.

My bad. Fixed now.