Method of joining granny squares . . Help!

[Mummybookworm]

I have 80 granny squares to join together (what was I thinking!). I have experimented and I want the blanket flat on both sides. The pattern said to double crochet them together but this left a bulky seam on the wrong side and I didn't like it. Any suggestions for alternative methods? It's looking like whip stitch at the mo - need to get myself in the zone for it though!

Hopeful bump . . .

Whip stitch. I did a blanket made of almost 1000 small squares that way.

Do any of these help?

Join as you go technique is good, especially if you want one colour to frame each square. I am currently using this method and it goes really quickly and you can crochet in ends as you go.

Mattress stitch. It's fiddly if you're not used to it, and takes time, but it's invisible. Whip stitch is good: not invisible but flat and quicker. You could also try crocheting with slip stitch instead of dc, there's still a seam but it's not as big, and it's quicker than sewing.