SketchUp Make 2017. The "trial" is just for the Pro features.
https://help.sketchup.com/en/downloading-older-versions
SketchUp continues working just fine after that, although you can't export the OBJ files that OOTP uses without an add-on:
https://sketchucation.com/pluginstore?pln=OBJexporter.
And, sure it's complicated, but you'll never figure out how to use it if you don't try.