Has anyone ever used a double needle when making a rag quilt? Any pros or cons would be appreciated. I would think it would reinforce and give more strength to the seams, but I am a beginner and am not sure if this logic hold true.

If it makes you feel more secure, go for it, but I don't think it is necessary. Just use a shorter stitch length and you'll be fine.

Thanks! What stitch length do you recommend?

Personally, I would just use a normal stitch that you would use for typical sewing. After you've sewn a row, turn it around and restitch. It's a great time saver to do it this way. I thought about the dbl needle, but using one will not give you what you are really after which is a double stitched seam.

The tiniest zig zag stitch will work too. Nancy Zieman calls it a wobble stitch. She narrows it to the point it is "almost" a straight stitch. :D:D:D

Using a double needle gives two rows of straight stitching on the 'top' and a zigzag on the 'back'.

Something around a 1.5-1.8 (that's how I can set my machine). Like Amma said, a really small zig-zag will also work. Comes down to preference.

Just make a sandwich out of some of your scraps and adjust down until happy with the smaller size stitch.