For one thing, cost of silicone sheeting large enough to cover the outside of the keggle mash tun will be in line with getting Line-X applied. For another, I'd either be pulling it off to clean the keggle, or have to figure something else out.
Plus, if I had them apply the Line-X to the section above the main body, where the handles are, it should be safe to touch with bare hands.
My other option is to get a welding mat/blanket (rated to 1800F), fold it over a few times, and secure it for use during the mash. It would be just shy of long enough to completely circle the mash tun. Plus, the fitting for the RIMS return would mess with things (with the silicone sheeting option too)...
IMO, straight Line-X or perhaps the previously posted foam and then Line-X on top of that, would be a better solution. Just looking to find out IF that configuration will be safe with a direct fire (propane) mash tun... I can get to the Line-X place on Saturday. IF I need the foam insulation too, then I'll need to place an order with McMaster-Carr with overnight shipping. I can only imagine how much that will hurt. Next weekend isn't an option for me, since I have truck maintenance scheduled for Saturday, and doubt that will be done in time to get to the Line-X place. Chances are, I'll be brewing either that day, or before the following weekend... So I'm under a bit of a time crunch here.