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…

SKETCHUP FILES:
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)

EXPORTED STL FILES:
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?