Have any pics of the bent aluminum sheet?
On my Honda VX I'd used a polyethylene water heater pan for the skirt material (similar to below), but the Jetta wheel well opening is larger than the largest pan I could find at HD. With a little support along the bottom, this was a great solution because it was thick enough to hold shape but flexible enough to absorb impact.
Alternatives might be coroplast or some other (flexible) plastic paneling... something that can take hard connection points while also being able to flex...