I happen to like glass tanks (but fyi, I keep things OTHER than BPs- NOT BPs), & I have to say that's not a good tank for a BP (even with the modifications mentioned). Your hunch is correct- it's too narrow- if it was a standard 40 gal. "breeder tank" (36" long x 16" wide x 17" high) that would be far more suitable in terms of the floor space- but still challenging to keep in the humidity. All housing options have pro's & con's- depending on what you're keeping & what you're willing to do to make it a good fit.
Incidentally, your tank would be GREAT for a corn or rat snake. As would a screen top for maximum air-flow. But I digress...
Handwashing & learning to correctly "read" your snake's body language should keep you out of trouble with your gerbils & snake in the same room. (Also, don't forget that your clothing can retain gerbil scent too, so if you handle them in ways that they're on your clothing, change clothes before handling a snake.)