I currently use the fithwum container and have two different mappings; one for the data (my worlds, uploads, modules, compendiums, etc.), one for the actual VTT software.
/foundry/data <--> /mnt/user/Foundry/
/foundry/fvtt <--> /mnt/user/appdata/FoundryVTT
Did this just to keep the appdata folder reasonable, as it is on the SSD cache array and my data folder is on the storage array (data folder is nearing 40GB at this point, so don't need all that on the cache). The server running from the appdata folder is fine though.
Thoughts? I'm not totally stuck on this - just made sense at the time with fithwum's config.