"New" bike new issues...I'm starting to order parts for a similar light as built before.

Problem 1.
The battery bag is a waterproof binocular case that hangs from the seat rails. What's the best light weight way to lift the bag away from my legs and stabilize the bag?

Problem 2.
The 35W bulb comes in 16.8V or 18V. For a 16.8V battery (that'll run a 2nd smaller light), which bulb is best?