Sorry late reply! Stupid steam does not notify me when there are new topics here. I think one of the most recent guides is made by tads, and contains several videos where a track is created and used in game. In combination with this there is a good modding document in the tools folder of Wreckfest. Combining these will mostly put you on right track, and alternatively you can also reach us (modders) at the discord group of Wreckfest through the modding channel :)

Thanks man!
Still hoping you upload your tutorials too. More stuff to learn from. :)

Is there anything for a demolition arena, too? Just find stock round courses.

Hmm, most of the same concepts apply, but there is an example event in mods folder of Wreckfest (example mod), which shows all the technicalities needed to make it work in game. It also includes a file structure which you can follow to get stuff into game. Some files has to be opened by the took bagedit, which is a tool within Wreckfest folder :)