Ken,
That is an excellent diagram. Showing off your artistic skills again huh? j/k.
One question tho? I'm not sure if you said you already had a multimeter, digital or otherwise (insert 'moving coil, needle type' here), to measure the RESISTANCE of the heaters?
Most Important.
This value is needed to calculate the CURRENT drawn.
(JIC.....To measure, simply connect the meter leads to each lead of each heater separately. Hopefully both heaters will be about the same reading in OHMS).
Alternatively, a digital multimeter can be bought for around $15. It should be capable of measuring up to 10 AMPS DC. Most Jaycar ones are.
This way, you can measure the current drawn by one or both heaters & the fan.
Most computer fans draw ~200 mA or .2 of an AMP.
Connect the meter in series with the fuse in the +ve line.
If the reading is close to or more than 1 AMP for
one heater, then I would go looking for a larger capacity power supply. Say, a 3 to 5 AMP one.
Keep us informed as that way, we'll know you're still kicking.
Regards, Laurie..