Do you have a segregated space for your cab? I am in the same scenario with the same temp swings,
You can do LED, its not that they dont produce heat- just nothing like HID.
Lower Temps are better problems to have than Higher Temps.. small space heaters at walmart are <10 bucks, but the reason I ask about the separate area- CERAMIC heaters, are more efficient at keeping a surrounding space to the set temp, digital panels/heaters draw the same on an off/on switch, new age ceramics will adjust their draw accordingly... I halved my bill from last month and that is the ONLY thing I can think of it being. (all lights/spaces/fans running..)
Anyways
A room inside of a room inside of a room....
Cheaper LEDs will heat up better
![Wink ;) ;)](/styles/smilies/icon_wink.gif)
but come summer you will be kicking yourself, my garage grow space hits 90s with 1000 continuous w's of AC, almost worth shutting down for the season... O wait