The Addon Manager works perfectly on any internal/external drive, regardless of where the simulator is installed.
In fact, we were the first to use the proper method of using an add-on.xml, and we are still amongst the few that use it properly, meaning not just using an add-on.xml, but having the installer supporting ANY path, instead of placing everything in the Documents folder (like some add-ons do), which makes the installer easier to create, but it's missing the point of using an add-on xml to begin with, since while it surely allows you to install outside the sim, it still restrict you to install into your main Documents folder, not any drive.
Our installers, instead, properly allow you to install *everywhere*, putting ONLY the add-on.xml itself ( NOT the files ) in the Documents folder, which is the only way to give you complete flexibility.
The problem you are having, it's likely because you first installed something from FSDT in a place, then you changed your mind and wanted to "move" on another drive. Unless you know exactly what you are doing, meaning you know how to manually edit ALL the add-on.xml files to use the new paths AND you know to edit the registry, it's best to use the following procedure, which is the ONLY one that is guaranteed to work, and won't require any manual editing.
- Uninstall all your FSDT products.
- Reply YES to the question "Do you want to Remove the Addon Manager ?" THIS is the MOST important step!!
- Repeat for each and every FSDT product you installed.
- Reinstall the first product. It can be any one, starting with GSX is just fine. You'll notice THIS time, the installer will ALLOW you to choose any folder you like, on any drive. This is possible ONLY because your replied YES to the Addon Manager question before which resulted in clearing a registry key that will "forget" the old installation path.
- Assuming you want to install in E:, then just choose E:, the installer will install into E:\Addon Manager, which is a perfectly sensible choice.
- Now install all the other products. You'll notice that, from the 2nd installation, you won't be allowed to choose the destination freely, because you decided it with the first install.
This method works, and it's the only way to prevent users from mistakenly install, let's say, GSX in one place, and KLAX in another. While we give you 100% freedom on where to install FSDT, ALL products are designed to STAY TOGETHER, that's why you are free to choose the location only after the first install.
All subsequent installers will read that location, and will create correct add-on.xml files.