I haven’t heard of a product called mount IFS.
You can use Operations Navigator to setup a file share on your AS400 then a windows server can map to it using the iSeries NetServer service. //servername/sharename
Your windows server could map drives to it or you could direct your web app to see the AS400 file share as the directory for your documents.
Instead of FTPing all the documents you could leave them on the AS400 reducing bandwidth consumption and the web app would only retrieve requested documents.
Warning on AS400 file shares – If your OS < or = V5R4 you will have issues if you’re trying to map drives or use ODBC connectors on an 64-bit Window client. (You need V6R1 or newer for 64-Bit connections).
If I miss the mark please provide some more details on your support website.