So I have seen Gullwings in G wagons (made by Frontrunner). The prior gen G wagons (1979 - 2018) have a very simple window design with the glass fitting into a rubber panel which lends itself to the gullwing also being a good simple design. I doesn't add any more noise..in whats an already very noisy vehicle due to the boxy shape.
However, when I look at the Grenadiers 3rd row windows, they look like a more modern sealed window design. So the gull wing panel looks like it mounts similarly with a sealed design, The opening of the gull wing should be a tad smaller with a door seal like design. No reason to think it wont be water proof. If anything the replaceable seal should make it serviceable.
As you can see from the images below, the designs are roughly similar but the window mounting styles being different lends itself to a slightly different gull wing design