Very rough calculation: assuming the RV is 5x2 meters that would be 10m^2 of solar panels. Solar energy that reaches the ground is about 1kW/m^2 at the peak, let's say that in a whole day we get the equivalent of 6h of peak energy (I'm probably overly generous here and not accounting for seasons and weather), and that the solar panels are 20% efficient. That makes 1x6x.2=1.2kWh per day.

The 4-battery version of the truck has a range of 400km with 448kWh of capacity, so that's 1.12kWh/km.

Putting everything together, running the truck on solar panels would afford a little more than 1km of range per sunny summer day of charge. To put it another way, a whole year of sun wouldn't be enough to charge the battery fully. So yeah, as tempting as it sounds, going full solar to power an RV that size is not viable. Even smaller ones aren't really either.