Small business using iPads needs to allow access to documents stored on office computer
I would use Dropbox for this, creating separate repositories for Sales and Installers. 

Any changes made on each device will sync back to DropBox, and any changes on DropBox will sync back to the individual devices. 

My business does this very thing with Marketing, and Sales. 

The one thing I see as an issue is that any changes will sync immediately, not based upon location (i.e., "when they return to the office.")