Your bike looks like a great choice for adding a TSDZ2.
Myself, I'd look for a rectangular battery that fits between the frame tubes like you were planning to do but the bottle type battery might be a great choice for you also. Depending on your planned use I'd stick to a 10ah battery - a 36v 10ah battery has lasted me 46 miles/3400 ft elevation gain with capacity left over - but I don't ride my bike like it's a electric scooter, which I see other ebike riders do.
EDIT:
If you don't mind the larger VLCD5 display recycles-ebike sells this kit including a 8ah seat bag battery for $500.
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