Getting UDB to work with Chex Quest 3

[nerdybunny]

I've taken the Chex 3 UDMF format from the Other Games directory and imported all the stuff already, but when I attempt to make a new GZDoom UDMF map with it using chex3.wad as a resource, I get a bunch of DECORATE errors:

 

I tried importing the original chex and chex2 as resources because I thought maybe it was trying to use the classes from those, but no luck. Everything else I've found online suggests that this should just work so I'm not sure what I'm doing wrong here.