Thanks guys.
I can add a zip-tie in the middle (just for extra piece of mind). I like the analogy of having the tubes part of the bumper and not just something jammed in a hole.
I can't comment on the warm-up time, as I'm not yet using my SGII and Honda cheaped out on a coolant temp guage. I'm expecting below freezing weather all the way into April so I'm not yet worried about high engine/coolant temperatures.
I've filled up my tank right after the grille block and so far I've noticed a decent increase in mpg. My avg was around 35mpg before and after the block it's been 40mpg, but I've only had it since yesterday and only made 2 short trips (10 min and 15 min, so time will tell.
Why do you think the foam tubes will only last one season?
Will the foam disintegrate from weather elements (UV rays, temperature, road-salt and grime)?
And another question for all the Honda Fit (2nd gen) owners:
Would blocking the upper grille be worth-while for mpg increase during winter, or would it cause heating issues to other components?
* The upper grille has a "honeycomb" type plastic grille insert with approx half of the holes filled-in and only half are open. The hood has a plastic duct that seems to take the air from the upper grille and directs it to the right-side at the back of the engine-bay. It appears to cool the battery, brake and clutch fluid containers and the engine-fuse-box (or some "black-box").