I searched for an horizontal only instax frame and haven't found any designs i liked. So i created this one. The instax picture is loaded from the bottom of the frame, so you don't see any slits while looking at the frame.

I've uploaded two STL files. One without supports and one with custom supports made in OpenSCAD. The custom supports neeed to be removed post printing with a knife or sharp side cutters but keep the overhangs from getting out of shape (hanging down) while printing.