
Help with how to create another part from existing part
I want to create a lid that follows the form of this existing part, with extrusions that dip into the part for a snap fit. I'm not sure the terminology to search for to find the best technique. Like an "inverse cavity" from another part, I want to partially fill in the existing cavities and connect them with a lid.
I tried to create an offset with a bit of overhang, but the fillets made things a bit weird and I couldn't select the right curvature to create a new extrusion to cap it.
Trying to avoid having to maintain all the dimensions of individual parts to keep them fitting together.