Thats a fair bit of power you the drain side of the FET now, dont forget to take into account that a FET has a bias point aswell, eg: as the FET turns on or off, it increases/decreases to an open/closed circuit - its not an instant change.
As this happens, the FET will develop a resistance in the circuit, and as a result, it will have a voltage drop over it, this means the FET is now dissipating power (V * I) in the form of heat.
This could lead to spike heating inernally to the FET that will degrade the FET much faster than normal (you are effectivly increasing the current by around 2 fold that it normally handles)
Soooo, everything else looks good buddy, but if the FET keeps "Blowing" in the future, you should attach a Drive circuit like this, or do it to be safe before hand
**broken link removed**
(Circuit shows a motor being driven and a logic level driver, but you get the idea)
This will turn your FET on and off much faster, and pro-long its life, if your grips are getting too hot, then consider attaching another resistive load to the series circuit