Well yeah... it would be... but I don't got no choice. The drivers I'm considering are the SoundSplinters and they are more popular for cars (trunks). I'd say it gets just as hot and cold in those as it does our attic. And yes... 120F is probably on the low side in the dead heat of the summer.
I've given some thought to building them inside the room in a baffle type enclosure... 2 drivers front left and 2 drivers front right and then 4 drivers in the rear across that back wall. The box would take up about the same footprint as the SVS but it would be a lot taller because I'd have to have some serious cubic footage. I could probably get close to 12 cubic feet per driver I think. It would no doubt clutter up my room, but who cares, it's an HT room. The location then would help keep the back waves in the room.
EDIT: Nope... scratch the thought of building a box and locating the IB's inside the room. You need about 10X the Vas of the driver, which on the SS drivers is 5+.... 50 cubic feet per driver.
You can get by with less and it still sound pretty good, but if you want true IB, 10X sounds like the magic number.