Yeah, it just looks like they extended the rear to partially enclose the parachute to make it look more like the stock model.
I'm sure they use it to help reattach whatever air they can from the roof to the trunk. Having a simulated longer trunk to help reduce the air bubble back there.
That's strange they'd use Ice water, I guess they're not going too far. For some reason when I heard Bonneville I first thought the race track and was thinking ice water wouldn't last long.
I wouldn't think a CO2 bottle and dispenser around the grill would be too heavy and would provides lots of cooling (like the CO2 misters for turbo intercoolers).