I don't feel right about trapping more heat around the bulbs myself. My suggestion is don't use a reflector at all and even try another brand of globe. I have a 40cm fan blowing a gale across all my bulbs so the ballasts are cool to touch. Out of 6 bulbs I only had one blow and that was within a few mins of turning it on.
The globes are 48watt (240watt equiv. energy saving). They cost about $18 US. each.
I thought flouros were supposed to last about 5 to 10yrs but gradually lose light intensity over that period.