I'm making every effort to understand Loft/ Flow/ Network & Sweep commands - how to utilize them to make a one-piece surface that wraps around a rectangular top frame (which has rounded corners) - and that the area INSIDE that top frame is the ONLY OPENING in the object!

I get what is sub-d modelling: https://youtu.be/ckOTl2GcS-E however, how far does Moi3d go in that direction to 'fake it?' ha-ha!

Example: