I have a 1x36 for my 10 gallon, and I passed up retro fitting into an existing light fixture for the same fears you have. I built a cheesy box out of 1/2 oak, mounted the ballast on the inner back wall and left a slot open above the ballast for ventilation.
It doesn't look as nice as a retrofitted light fixture or a box made with good tools, but I'm confident that it will not melt anything, or heat anything to the point of combustion. You could also mount the ballast on the outside with some kind of stand-offs to keep it away from the plastic. Again, not pretty, but safer.
It doesn't look as nice as a retrofitted light fixture or a box made with good tools, but I'm confident that it will not melt anything, or heat anything to the point of combustion. You could also mount the ballast on the outside with some kind of stand-offs to keep it away from the plastic. Again, not pretty, but safer.