A mash tun (or lauter tun) can be made very inexpensively by converting a rectangular cooler for the job.
All you would need is the following:
One 48 qt or large rectangular cooler (mine is a Coleman brand)
One #2 stopper
One bottling spigot
Three feet of 3/8” soft copper tubing
All that needs to be done is this:
1) Remove the drain from the cooler and replace with the bottling spigot.
2) Bend the copper tubing into a shape that will fit into the back of the bottling spigot and cover most of the bottom of the cooler without coming close to the walls of the cooler. Use a pair or pliers to crimp the free end of the tubing.
3) Cut slots or drill holes in the copper coil.
4) Put the copper coil into the stopper, and the stopper into the back of the spigot.
After mashing, use the spigot to regulate the flow from the tun during the vorlauf and the lauter. You can use the same method to convert a bottling bucket into a lauter tun. I mash in a converted Sanke which is directly fired from a propane burner
And then I transfer into the cooler for the lauter following the mashout.
Using the copper coil shown below, I routinely have 80-85% efficiencies.
Here is a picture of the bottling spigot where the drain used to be. I attach a piece of 3/8” tubing to the spigot to avoid splashing the hot wort during runoff.
Here is a picture of the copper coil slots. I used a borrowed Dremel to cut the slots, but a hacksaw, or a drill could be used as well. Remember that the slots will be turned down, and the coil should be made to not touch the side walls of the cooler to avoid channeling the sparge water.
And here is a picture of the inside of the well used mash and lauter tun with the coil inserted in the back of the bottling spigot.
I have found that the heat will deteriorate the spigots over time, and they will need to be replaced. I also found that on some coolers the spigot will not fit and the drain hole will need to be drilled. If the seal is not watertight, you can use DAP Silicone Sealant (it is food grade after 24 hours) to get a seal, but on the Coleman cooler that was not necessary.
Here is a picture of a drilled coil I made for a bottling bucket. I have gotten about
the same efficiencies using it for low gravity beers where the grain depth would not be sufficient to effectively use the rectangular cooler.
When I use this coil, I still mash in the kettle, but I transfer the mash to my old bottling bucket for the sparge.