I figure I would catalogue my findings and put them all in one place in case anyone else is looking for the models in this game.
This wouldn't have been possible without the help of TeaEffTeu, who provided the QuickBMS script used to extract the .npk files.
You can find the script here
The process is as follows
Once you install the game you have to locate the .apk files buried in your phone or emulator, turn these into zips so you get into them.
Inside the split_mini_client and split_mini_client_extra apk/zips there are asset folders, the .npk files can be found within.
Run the quickbms script, follow the instructions and select 0 to force decryption.
Run RMAViewer to view the .dat files that have been extracted from the .npk files.
From the RMAViewer interface you can extract into .obj files.
I do have an issue when trying to find certain things in the files. I can only find the low LOD models of certain units as it looks like RMAViewer can't open some files. If you can figure this out, I would be most thankful. I have an example file listed in the comments below.
RMA_Upd3.zip