Elescher,...that looks interesting though the link above did not work until I tweaked it a bit;
http://www.soundstringcable.com/gen2/Bulk-Delta-3-12-High-Out-put-30-Amp-Power-Supply-Cord-Power-Cord-Cable.htm
It looks in-wall rated at seems to be 10-gauge. Let us know how it works for you as it could be a nice, more cost effective alternative to Romex.