Design for waterproof 3D objects

I’ve been designing a waterproof case in Sketchup, and attempting to print it using cura.

I group my design geometries, and I know sketchup doesn’t have a concept of depth, only zero thickness surfaces… but is there any trick I can use to achieve/induce 100% infill in some parts of the design itself, while leaving the remaining parts of the design to whatever infill % the slicer has set?

I have coarse control over it from the slicing program… but not sure if I can do something earlier when designing the model itself.

It would help if you’d share the model so we can see what it is you are working with exactly.

tier2_module_generic.skp (13.5 MB)

Thanks Dave. I’ve attached the module housing. Oring can be printed or just use raw 1.75mm TPU filament (groove dimensions are to suit 1.75mm diameter oring) and the lid is completely flat and gets screwed on top.