Yes, FastPlastic, every little bit should help ... and since you are doing it yourself on a shoe-string, you have practically nothing to lose.
But I have to side with the others here that your roof rack is a killer. I'd remove it ... and if you have bolt holes going into the roof, take the bolts that go into them, give each a dab of RTV silicone on the threads then replace them. They shouldn't leak for 20+ years.
My uncle has a Hyundai Tucson with a long commute he complains he gets only 23mpg. I told him to at least take the cross-bars out of his rack (which is never used) and inflate the tires to 2psi lower than the sidewall maximum ... that might get him to 25mpg ... but I know he won't do it. Some people are funny like that.
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--- Bror Jace
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