Hi @ScanIT,
Welcome to our community!
It is possible to use Reach RS3 as a base with a Trimble R12i rover over Emlid Caster. This Trimble model meets the criteria of the Emlid Caster, so it should work fine until you have stable Internet connection.
But @Wombo is right. If you want to broadcast the correction via LoRa, you need two Reach receivers, so it won’t work with the Trimble unit.
Regarding the apps, as far as I know, you can’t use Reach RS3 with Trimble Access, but maybe it’s worth the double-check with Trimble. But overall, if you want to use the Reach RS3 as a base, you don’t need much to do in Emlid Flow. You should just set up your base by averaging its position or setting its coordinates manually. After that, you should enter the credentials of the mount point from the Emlid Caster page, and you are done. You can start surveying with the Trimble receiver using Trimble Access.
But you mentioned that you prefer to use Trimble Access. Do you miss something from Emlid Flow that would be essential for your work? Your insights would be valuable for us to determine the future steps of development.