Boulder Creek has been making clothes for big men for a long time, and they are thankfully consistent with their sizing. One of the biggest problems I have had with ordering clothing online is that a 6XL can mean wildly different things depending on what country and brand is producing it.
King Size sent me this Camo print hooded shirt jacket, and just from the brand I knew I wasn't going to need to worry about the fit. As far as the shirt itself, it is warm without being too heavy, and the sleeves button securely but are thin enough to be able to roll them up if you need to.
If you are looking for something to keep you warm but not too hot while working outside that will wear well and fit the way you expect, this shirt will do the trick and keep you comfortable in Fat Boy Heaven.