Hi Ken................................ ...........th,
The third diagram on right will work just fine.
Make up a heater to be a little 'warmer' than you think, then duplicate it.
No problemo.
You've just "completed a parallel circuit".
L.
ps. After finishing your heater, try wrapping it around your arm to test for temp.
You'll soon know if it's way too hot. hahahahahaha..
pps. I'd forgotten all about my 'alligator/crocodile clip' trick/post, errr, way of getting the correct temp.
ppps. A PWM (Pulse Width Modulation), unit will let you control the temp more accurately. Cost about $25 odd?? Not sure, as I make my own for lot less, as you know.
Would you like one? Only cost ya $40....