Exporting for 3D Printing (STL or OBJ)

I have 5 parts that I am trying to export for 3D printing. I can use either an STL or OBJ file. I have deleted all of the guidelines and the design is solid. But when I export, the files are not clean at all. Any advice? Attached are the files, FYI…

Motor Mount.skp (156.1 KB)
Platform revised.skp (157.3 KB)
Prop Strut Revised.skp (100.1 KB)
Cover revised.skp (135.3 KB)
Hopper.skp (205.9 KB)

Motor Mount.stl (581.5 KB)
Platform revised.stl (703.7 KB)
Prop Strut Revised.stl (140.6 KB)
Cover revised.stl (411.4 KB)
Hopper.stl (646.6 KB)

I opened your Motor Mount in Cura and it seems fine.
What problems is it showing for you?