Is there any problem if I solder standard 12 gauge wire to extend the

Is there any problem if I solder standard 12 gauge wire to extend the heater cartridge wires off the hot end?

Nothing is wrong with that. 12 gauge might be a bit of overkill. Cartridge is 40W so it is less than 4A in any case

Should not be a problem. Just ensure you have a good joint, and avoid solder joints at areas where flexing will occur.

Great. I am printing out a smoothie board mount right now and will hopefully complete wiring tomorrow.

http://www.instructables.com/id/Master-a-perfect-inline-wire-splice-everytime/ Learn the lineman splice and solder the wires like that. Much nicer finish.

20ga should be plenty.