I know I’m a bit off the main stream, but I use a cheap 5gal SS stockpot to mash in and set it into a styrofoam box (Dow blue foundation insulation board sheet cut and glued with siliconized acrylic latex). This keeps your mash in SS and I only get about 3 deg drop in 2 hours. I mash-out and then transfer to a SS lauter tun I made (by scooping the mash and layering on the screen). The coolers are not rated for hot liquids (see my web page info) and are most likely leaching nasty chemicals into your wort. My SS lauter tun was pretty easy to make, not expensive, and drains very well and efficiently. The drain is on the bottom, where a drain should be… I tried to get the NB folks interested in supplying them but they persist with pushing the picnic coolers… This is really simple to put together. After pouring in the mash, I recycle <4L of the initial runnings and it is running clear and bright. Good flow rate, good extraction efficiency. I know the separate kettles and scooping isn’t something that scales well, but it works fine for 5 gal batches and that is what many of us make.
The info is here, sources, costs…http://people.umass.edu/dac/projects/la ... erTun.html