I'll second the recommendation to get the SG. If fuel economy is something you're really interested in, there's absolutely no question about having one. Just do it.
Hours of entertainment, and it'll pay for itself.
As for the blocking technique: note the bigger advantage will come from blocking (some) air from entering the engine compartment in the first place, not just from stopping it from passing through the radiator after it's already come through the front. If you're going to experiment with it, block the grille itself.
Anyway, welcome to the site. I haven't been to Wasaga for years. Last time I was there I was in university (figures!), driving an old VW Rabbit (as efficiently as I knew how at the time, of course).