You can do this using an (experimental) portable project. Basically, you will have to:
- (make a backup copy of your project file)
- move your project file to the folder where you currently keep your photos
- start Tropy, find your project file and open it at the new location
- enable developer mode in the preferences
- and, in your project window, select ‘rebase project’ from the developer menu (just once!)
- disable developer mode again and close Tropy
At this point you should be able to move the entire folder, containing both your project file and all the photos into your Dropbox folder and let it sync. Once downloaded, you’ll be able to open the project on a different device. Going forward, you’ll have to be very careful not to work on the project at the same time from multiple devices or one device will overwrite changes you made on the other device.