Working really well on my Manjaro KDE 3-monitor setup. This is well worth a try and the best one I have seen so far. To start it automatically just add the app to your AutoStart apps and ensure you had set the app up correctly and saved the profile. After that it will start with the last used profile. If you have unticked the show help on startup, it will just open silently in the tray after startup.
See Superpaper 2.0 is an Advanced Multi-Monitor Wallpaper App for Windows & Linux – OMG! Ubuntu!
I wrote about Superpaper, an advanced multi-monitor wallpaper tool for Linux and Windows, last year, finding it particularly good at what it sets out to do.