For the 150$ you would waste on that to cover up the metal where your seats bolt in etc, you could buy 6 tanks of gas.
Keep your foot off the gas as much as possible and just don't think of buying things to "Improve" gas milage, cause the money your most likely wasting on them can just be simply spent on gas.
And think about this, say you spend 100$ on something that gives you 1extra MPG.
Just think of this, if u have a 10gal tank u get 10extra miles per gallon, so instead of 100 you get 110 miles per tank.
If each tank is 20$, then it would tank over $200 in gas already to even save yourself a $20 tank of gas. So you would have to spend roughly $1,000 in gas anyways before it even paid for itsself.