It is very easy to get it into Plasma, but Plasma insists to manage background
of the root window (pkill plasmashell), and it doesn't even have a capability
to set different backdrop or picture to different desks.
(Read, cry and think how happy you are with FVWM!
https://forum.kde.org/viewtopic.php?f=67&t=141878 )

You should probably move or remove redundant KDE dock which covers FvwmButtons
Front Panel.
