Mobile apps have the potential to support collaborative fieldwork even where web connectivity is unreliable or unavailable. To explore this potential, we developed portable network infrastructure and custom-made field tool apps. We deployed this solution in remote communities in the far north of Australia, in connection with co-located cooperative language work. Throughout a series of visits, we worked with community members to iterate the designs, optimising their suitability for the tasks and the context. We found that custom toolmaking provides the benefits of digital collaboration tailored for the specific needs of the environment and community. However, we argue that it is activity design -- not the technology itself -- that must be foregrounded, placing fieldworkers in the driving seat of innovation in digital fieldwork practice.