You may want to configure the U-blox chip if you're using a dedicated telemetry link to connect your base and rover module, instead of encapsulating it in the MAVLink protocol.
You can use the U-center software in order to configure precisely the behavior of the M8P chip so that it will achieve exactly what you want.
In order to configure the rover, you'll need:
1 Computer, used as ground control station
1 Micro USB cable
Latest version of U-Center Software (available here)
Configuring the U-blox chip
First of all, install the U-Center software on your computer. When done, you can connect your rover module to your computer. Open the U-Center software after that, and connect it to your rover module module using the button in the upper-left corner.
After connecting, you should be able to enter the Configuration view from the top hotbar.
After any modification made in the Configuration panel, always remember to hit the Send button at the bottom of the configuration view panel, or your modifications won't be stored!
In the Configuration panel, scroll down to the PRT (Port) section. Here, you need to enter your autopilot's GPS port's baudrate to allow it to communicate correctly. It's necessary, as the link between your GPS and the telemetry is purely serial, and there's no other protocol to stipulate a baudrate.
It's also necessary to modify the frequency of the chip. To do this, on the left panel, look for the RATE (Rates) menu and modify the Measurement period to 200 ms.
Don't forget to click Send!
Next, get into the MSG (Messages) menu and disable all NMEA messages.
After disabling the NMEA messages, you should also enable the following messages for the UART1 link:
To do so, find each messages in the droplist and check the UART1 box for each of these messages, without omitting to click Sendfor each message.
Modifying the dynamic filter can also help. You can change it in the NAV5 (Navigation 5) menu, using the first droplist at the top of the menu.
After doing this tweak, save the whole configuration you've done, by getting into the CFG (Configuration) menu on the left panel, selecting all four memories on the right, and clicking Send.
Now that the configuration is stored into the chip, you can disconnect your RTK module from the computer and plug it to your autopilot!