The procedure for creating new terrain has changed. See page 34 of the guide.
I have no idea on why your map(s) won't work on the Steam workshop, but work(s) with JSGME. Sounds like I need to try JSGME though. Because that would be awesome if it was the workaround to play manually installed maps with version 18/03/06. Unless I'm not understanding what you're saying, and it doesn't work like that.
@mudhappy Kids dont read these days, im only 21 and im feeling quite old just because I do read guides lol
Edit (05/04/18 23:48) Mine is broken now too, I went to upload some truck mod files and my editor crashed every time i want to generate a preview or just upload the mod
@Forces It's still working for me. I just uploaded some ST to MR conversions with it. I'm running game version 29/01/18b. Not sure if that makes any difference.
@joridiculous Evidently so. Since using it to install maps with game version 18/03/06 didn't work any better than manually installing them. As in it doesn't work at all in either case.