Hello Andy,
I did download and install this LANDCLASS files.
What I have done and it works :
I have all VPC/California sceneries (airports) and textures in 1 folders with highest priority
I have a California Landclass folders (only scenery) just below = less priority
I have the LC_CAV2 landclass folder (I did rename it " California Landclass lowest priority" , only scenery) almost at the bottom of the priorities.To my understanding a LANDCLASS bgl file may NOT be mixed with sceneries ; it may not be in a folder scenery associated with a texture folder . If you do so the game will "eat" all your memory up to an FS9 error message.
See AVSIM :
Microsoft Flight Simulators MS Flight Simulator General Discussion Forum topic #175241; Your computer has run out of memory, FS will now exit..."
Hope it helps
Regards
Emile
EBBR Brussels
Belgium