I'm with Tucson Jim... 10 AWG stranded is just fine. When I built my rv garage, I used #6 AWG stranded for 50amp service from my house CB panel to the sub CB panel in the garage. From there I ran #10 stranded up and over and down the other side of the garage (about 75') for the 30amp outlet that I use to keep the motor home batteries charged and to use items in the motor home when needed.
I had contacted the building inspector prior to using this wire (it also was some left over stuff I had stored) and he said it would pass code easily.
I've found that most states have pretty much the same building codes when it comes to the electrical. That said however, you should contact your local building inspector and get the correct answer from him/her.
Ron