Yes, you can extend the length of the outdoor antenna, preferably with a type LMR-200 low loss cable. One end must be a RP-SMA-Male connector and the other end is a RP-SMA-Female connector.
Ask your reseller about it so you are always supplied with the correct cable if needed. Some resellers may offer different length depending on your need.
It is advised to be discreet when placing any antenna outside your camper or caravan. There is a growing trend of campsites that disapprove of campers using wifi amplifiers and may have private policies to deny you of their wifi service. In most situation, it is more than sufficient to use only the supplied indoor dipole antennas.