I just finished building my 11x14 a while ago and I needed to find a way to carry it. I have been using a rolling tool bag that I got from Harbor Freight and it works OK but I love to get off trail.
I have an extra large Kelty external frame backpack that I was going to use for my 8x10 system and I decided to go with my newer REI pack. The Kelty was sitting idle. This morning I was taking it apart when I discovered that I could take out the "U" shaped frame piece at the top of the bag and it would expand much more (DUH!!)
My entire 11x14 system fits. Camera, 2 holders and darkcloth in the main compartment and 5 lenses and the rest of the stuff in the outside pockets. I still have a little room left. I think it weights about 40-45 lbs. but feels OK on my back. Yes I know that after a mile or so it could be a different story.
If anyone has an 11x14 and is looking for a cheap way to carry it try an XL Kelty external frame pack. If you want some pictures added to this post let me know.
I'm headed to the Redwoods in October and now my 8x10,11x14 and 8x20 all have backpacks! I'm so stoked!!

Jim