(english is not my first language, sorry for bad english…)
i made some 3d model with bezier spline plugin.
while i work that, i deleted surface of bezier spline inner surface.
after that, i made surface by drawing line.
it looks okay, but if i trying to slicing by cura program, it make some error.
FWIW, you could change your workflow to avoid creating the internal faces in the first place. Start by drawing only the features that would be visible on the bottom face. Then extrude to the height of the lower inner surface before adding the curves that define the rim. Extrude the rim and you’re done.
In a case like this my thought process for that part of the model would be to think about how the printer would print it. The printer will only print the overall shape with the piercings until it gets to the height of the lower inner surface. Only then will it start to add the outer raised area. Do the same in SketchUp.