After a few unsuccessfull attempts I’ve finally found a way to use all the maps of Arden Vul megadungeon provided by Expeditious Retreat Press in a way that is suitable for online play in Foundry VTT. For some of the external areas I’ve included the isometric maps drawn by Jason Lutes.
In order to use the maps you need to unzip the folder into your FoundryVTT/data/modules/ folder. You also need to install the simple fog module and enable it.
Enjoy!