I thought this would have been as simple as adding vehicles, but apparently not.
I can't figure out what I've got wrong; I tried adding a simple Ore Silo-type structure that would also act as a cashtrickler, but I can't even reach the shellmap before ORA stops working. I've placed the relevant SHP files in the 'bits' subfolder (prfr, prfrmake, prfricon), so it's more than likely some text-based shenanigans going on.
Here are my defs, with the SHP files as an attachment:
If the game ever crashes, exception.log (Windows: You\Documents\OpenRA\logs) reveals some pretty good information
Trying your yaml & crashing the game, I got this in my exception.log: System.IO.InvalidDataException: Duplicate key `Building' in MiniYaml
This means you have the Building: trait showing up twice in your definition for PRFR. Here's the changes. If you have the proper SHPs like prfricon, etc. this will work