Many people with K-bikes find an uncomfortable amount of heat coming at them from under the tank. In the case of LT/RTs this is particularly troublesome because of the wind protection and particularly galling since the fairing contains obvious exhaust vents for this hot air. Unfortunately they are poorly designed, and they look neat, but are essentially nonfunctional.
The three steps described will reduce this problem to a minor annoyance, at a parts cost of about $150. They can be applied separately, but work better as a system. I have them on my K75RT. They can be used with/without a riding suit, which alleviates the problem all by itself for many.
1. K-guard heat shields reduce the amount of hot air coming at the rider. These are plastic sidecovers which fit below and behind the tank, replacing the small alternator and coil covers. On an LT/RT they fit up to the inside rear edge of the fairing. I think they improve the looks of the bike by cleaning up this area; mechanical purists may find even this small step toward covered mechanicals objectionable. The shields fit fairly well, but their function can be increased by sealing the edges with some kind of weather-stripping. I used half round pieces of pipe insulation. Note that some are concerned that keeping this heat in will fry the fuel injection computer. I'd rather the computer takes the heat than me. YMMV, especially if you have an 1100 instead of a 75. The air wings counter the problem to some extent.
2. Baker air wings screw to the fairing edge. They can be pivoted out to deflect air around the fairing at your legs, or pivoted in in cold weather to simply do nothing. It's very much like rolling the windows up or down. Drilling two holes is necessary on each side to screw the brackets in. Easy to install and use, and quite strong/secure enough for their purpose. They look a little funny, and come in clear or colors.
3. This step is simple and cheap. BMW rubber kneepads give a little insulation from the tank (which is also slightly cooled by the air wings) and space your knees out just enough to help the air wings circulate air inside your legs. They do tend to pick up an annoying white powder look if you are not incredibly careful about wax.
Your dealer should be able to help you find all of these products.