Bottle heaters cure the problem with initial bottle temp but cant overcome the drop in pressure during use when you are on big shots of gas.

I get round the fuelling (as wizards of nos would recomend) by using a wet kit with its own fuel supply and you set it up for the worst case scenario so the rest of the time its too rich, safest way to do it, the thing is with nitrous that the potential gains are SO enormous that its not worth chasing down every last BHP from a given amount of gas, its normally safer to jet it rich and then just go up a jet size if you want more power.
Not the most effiecient use of gas but nice and safe for your engine.