This appears to work fine on 1.8 as is from just some basic testing @MOARdV I did go through the effort of compiling DOE against .NET 4.5 and Unity 2019 assemblies if you're interested, it was pretty straightforward so i'm not sure if it's PR worthy. I could throw in a version bump as well, all you'd need to do is compile it yourself and create a release if you're up for it.
Is B9PS supposed to add tank types to default 'vanilla' engine tanks? Like LFO/LF/Ox.
I only have B9PS, ModuleManager, and Community Resource Pack installed, and all updated to the latest versions for 1.8.1 Player.log KSP.log
Not sure if this is a B9 issue, or a IFS issue, but there isn't any options on any IFS tanks in 1.8.1.
I only have IFS, B9PartSwitch, CommunityResourcePack, and ModuleManager installed, all latest versions. Player.log KSP.log
It's not, the new version of KS3P actually has an in-game editor now as well, might tickle your fancy tbh.
New version of KS3P has a completely new configuration setup, tried my best at simply copy-pasting your config to the new one without much luck.