Piece of cake.
First, get your Freeway Blasters from Ryderfleetproducts.com they're by far the cheapest on the market. I think I paid 22 bucks shipped to me for the 2 horns.
http://www.ryderfleetproducts.com/cgi-bin/ryderfp/search/srm/search_type/MFR/search_criteria/T37/erm/product_search_results.jsp
Then, if you know how to wire 2 horns with a relay and reuse the stock horn switch, do it. Me, I didn't want to bother so I bought a dual horn plug and play relay harness kit from Eastern Beaver. Great product, fast shipping, despite the fact that the guy lives in Japan!
Took 10 days from the day I ordered to receive it.
http://www.easternbeaver.com/Main/Products/Horn_Kits/horn_kits.html
Now, for mounting the horns on the bike, use the brackets supplied with the horns and the torx bolt that goes through the chrome fender trim and attaches the front saddlebag fastener and the seat strap bracket. Do that for each horn (1 per side). This will position the horns between the side covers and the shocks, high enough so that the left horn will not hit the belt on a bump (don't ask me how I know. lol). Once everything is tightened, push the 2 horns in (towards the rear wheel) so that they don't touch the back of the saddlebags. Mine are 1/2" away.
That's about it. What's left is to run the wires to the horns and horn switch and that's pretty well described in the directions from
Eastern Beaver.
Oh and I took the stock horn off but kept the cowbell on the left side. It's where the stock horn wires and the new harness connect and everything is hidden behind.
Feel free to ask questions if I wasn't clear enough.