Instead of doing anything that might impede your exhaust flow you can use hose clamps and a metal plate for the surface, make sure its good and snug, or even weld a small plate to your header. I think these can be ran in series or parallel to increase voltage or wattage output. Used with a charging circuit you can charge a battery. Check out the camping generators that you put over a campfire or stove that has 5 volt usb and 12v cigarette lighter outputs. Its being done elsewhere with no issues getting the voltages desired. You just need to figure out the operating tempuratures of what you intend to mount it on and buy the ones that operate at those tempuratures, then buy or make a charging circuit to cover your needs. Also remember, these will continue to generate electricity even after your engine has been turned off till it matches ambient tempurature. Also from what I understand is there only has to be a tempurature difference, you don't need it to reach a certain operating tempurature, those are just the maximums. Each one has different max tempuratures, some use solder so they can't get too hot, others have different materials used. If one side is 50C and the other is 150C they will have a 100C difference and get the power specified for that difference. If you can't keep the heat transfer at bay the cold side will slowly rise and it'll produce less. I might buy a few of these 99 cent ones and screw around with them a bit.