The tanks are in the belly below the floors. Take the belly covers off from underneath. There are a lot of screws that hold them to the frame. With them down you will get access to your tanks. the layout will vary depending on model. There is room to put insulation around some of the sides of the tank but I don't know if you will be able to get much if any on the top and bottom. I also don't know about the blanket. You may be able to mount it on the bottom and still get the belly pans on. don't know how thick they are and how they mount. You may have to pull the pan and check things out for yourself.
Roger & Cheryl Full Time since 2002, RVing since 1975 2008 Chevy 3500 Crew Cab Dually, 2012 RW 36RL