Nothing in the text indicates that the Warding spell is functional when cart is moving.
As I understood it when I read Griffin Mountain a long time ago, the Warding spell was for static protection only.
As a GM, as soon as one of the wands moves, I rule that Warding spell ceases then to protect.
It is interesting to see that the RQ2 Companion (included in 2016 RQ2 edition quoted above) indicates
But it seems RQ3 & RQG ignored the Companion, being just a copy of original RQ2 text...