ArduBoat configs

Hi guys, I am new into ArduBoat. I wish i could take advises from experts. i want to know two things mainly.

First, which will be best GPS[RTK] module to setup, real time navigation by offloading the map on ardupilot/aruboat firmware. Does it require any config in firmware. AS well as, is there any requirement to customize rover firmware for ArduBoat, coz i have a doubt like as rover runs in wheels and boat moves in using Thrusters. Information on this will be helpful. Thankyou. (And i may have more to ask in future.)

I can tell you the rover code works just fine on certain boats/ hull types. The tuning is a bit different