Hi Al - to fill in an area like that really needs a NURBS tool called "N-sided patch" which MoI does not currently have.

The easiest way to get what you show there done right now would be to use Rhino along with MoI and bring the model into Rhino and use its N-Sided patch tool to fill that in.

I want to add that tool into MoI in the future - it tends to be a kind of finicky tool to get right though, it tries to kind of warp a single surface into place and it's difficult to get a mechanism that does not make waves and undulations in the generated surface.

But instead of leaving that kind of empty hole to fill you can get a similar kind of result using the boolean intersection method I showed earlier - instead put some fillets on the box part before you do the intersection something like this:







Then apply some fillets to round off some of the sharp edges:



It's not the exact same shape as the method you showed, but it's pretty close and it's a lot easier to create. It's really difficult to fill in a hole like the one you show there without N-Sided patch, so if that's the one that you really need then your best bet would be to use Rhino along with MoI to get that result.

- Michael