You would connect the NMEA 2000 cable from both units to your established NMEA 2000 bus. If you don't have an established bus, you would need to build one. For just these two items the bus could be as simple as using our Furuno FI-5002 junction box. You will find example interface drawing under the TECH INFO tab of the GP33 product page.
The bus could be a backbone can bus with power supplied and terminators correct, using all cables and no open circuit board type connections. Therefore no need to mount a box. You can add can bus T connectors with drop points as needed. Terminations applied as per the can bus design and power supplied at the can bus design.