I thought the SD6 was also an 18650 cell type? I don't know whether the 18650 is particularly susceptible to heat, have you checked? The reason I ask is because lithium primaries are often recommended for high heat applications. I don't know the difference rechargeable LiIon chemistry would make from primary Lithium cells in this case.
I'm interested in your question because I also live in a hot climate and sometimes my gear gets left in the car or in the sun. Heat is death on many sorts of batteries.
I often use an externally stored alkaline primary for those lights exposed to heat--because it's painless to toss an AA alkaline, they're so cheap. I've not yet had an alkaline leak OUTSIDE a device. They always seem to leak inside, particularly when there's heat. So I just keep cells the heck out of devices that are stored in the car. Or, I go with lithium primaries.
If you're looking for a floody, you might check out the SD52, a 2AA light from Spark? It's reasonably bright, although not so much more than the 1AA zebralights.