This slim door stopper can be printed in less than 30 minutes, and with a few magnets, glue and double-sided tape, they can be installed and removed in less than five minutes (minus glue drying). I used 2 magnets in my first print, one on each side, and it was fine but kind of weak. I doubled it to 4, two on each side, and it holds all the interior doors. I went nuts and added 10, five on each side, and it reliably holds my front door, too.

In the files, I've included the stl files for both the flat version and the capsule version. I originally made the capsule version first, with the thinking that like wood, this would benefit from more surface area contact. That is not necessarily the case here, but maybe someone will want that one or can fix my design. 

There's a possibility for variations in the future, and I can upload larger sizes or make it parametric (if someone tells me how), if anyone is interested.