I bought a heated seat for my RS and am in the process of getting it ready to go. It's not trivial and it's not hard. Basically there was a Gen1 and a Gen 2 high and low seat. The Gen 1 was smooth, the Gen 2 has reinforcement stitching, I bought a used Gen 1 seat off ebay. So first you have to decide if you want Gen 1 or 2 or don't care, then you have to decide if you want the high or low seat. All the seats use the same plastic pan underneath just like the one on yours and my RS. The GT uses the same pan as well with the two slots for the high and low position. The GT low seat is the same as the standard RS seat, except it has a little hump for the passenger and it's a bit wider, therefore a bit more comfortable. The high seat has an extra one inch of padding, its about 2 inches thick compared to the padding on the RS/GT low seat. So it comes down to what is your inseam and what riding position do you like. I am 6 feet even with a 31 inch inseam, I use the GT high seat on the low position, which is the same as the RS/GT low seat on the high setting, but I get the extra inch of padding so it's more comfortable than the RS seat on high
There is a high on ebay right now, I have been communicating with Phil the seller, he wasn't sure which seat it was, so I helped him sort that out, it's a GT high (PN ...1846) like I already have. Also I don't think he has tested it to see if it works yet, you need to take an ohmmeter and probe brown(ground) to blue and hope to get about 15 ohms, which translates to about 10 watts, the low heat setting, and then probe between brown and black and hope to get about 7 ohms which translates to about 20 watts,the high heat setting.
So after you figure out which Gen, and which seat height you want, last you need to figure out how to hook it up to your RS. There are a million posts on this site about it, I find J. Northways posts and Razels posts to be the most informative. Basically you need to decide how many levels of heat you want, and if you want to put an LED indicator into your dash, buy a switch and the LEDs, figure out how you want to hook it up to the battery, and away you go.
Info from Lee from a previous post on seat height:
Here are some seat heights from a BMW Brochure.
30.3" & 31.5"
Low GT seat
30.3" & 31.5"
High GT seat
31.1" & 32.8"
and I have a pic I got from James showing the diff between the RS seat in the back and a Gen 1 GT seat with the hump, and a pic of a Gen 2 GT seat with the stitching. Also Razels excellent explanation of the wiring. There is also an excellent diagram I think by J. Northway which shows how to wire the thing up, I am looking for it. It's on this site somewhere, I have a screen capture I can post, but he has a Word document also.
You can choose up to 4 heat settings as per Razels diagram, the way I am doing it is to have two positions, 12V to blue and brown ground for a ballpark 10W low heat setting, and 12V to black and again brown ground for a ballpark 20W high heat setting.
As Einstein said, I have built upon the shoulders of giants who came before me.
There, that oughta keep you busy for a while
Next you will want to know about PTTR and the 5.5 inch wheel. Wouldn't mind seeing a picture of the Honda also, that's a great bike too.