I didn't think to check the calibration of the thermocoupler or the temp gauge ( duh). The mash vessel is the 10'gal igloo cooler modified with a false bottom.
I've constructed a rims system and have made several batches of brew. All have come out well albeit a bit inefficient. I have my pid set temps for either step brewing or single conversion. The tube keeps the temp in the tube spot on. The cooler (mash tun) is always about 10 degrees cooler...
I used a piece of 1/4" plexiglass (eBay). The plexiglass acts like a raised base within the cabinet. Mount by drilling holes through the bottom of the box. Use rubber grommets to separate the plexiglass from the base. Be sure it's raised up enough to allow small mounting bolts not to contact...