@alice @benhamill While I don't own a 3D printer I have worked with prints via friends and shops, and generally I print and then sand and paint it by hand. Makes for good, smooth results.

As for weighting it, the printing software usually fills the inner space with supports to strengthen the object structure. You'll have to specify an intentional empty space for the weight. If possible, print the object in 2 parts that snap together so you can get the weight inside it.