Hotter than behind the rear cylinder bank/exhaust headers, bolted to the inside of the subframe, under the seat, behind a side cover? And then maybe down in a pocket?
Of course as cool as possible is best, but unless you want it hanging from a rear grab rail or mounted to your lower triple clamp, I don't think there is a ideal solution on a VFR. I don't want either of those things. These bikes produce heat and things have to deal with it. I really don't want my carbs and air box right behind the hot air coming thru my radiator either, but it has to be "packaged" somewhere.
I've thought of mounting one on the back side of the rear fender, but I don't really want a wire run that long. And if it's a bike that's used in any weather, it better have some really good plugs / connections to deal with a constant spray of nasty water. And a lot of my bikes that don't go in rain don't have full rear fenders anymore.