I like a top loading back pack for my 4"x5" Speed Graphic or my 4"x5" Graflex Model D or my Hasselblads with many lenses [I have three packs]
http://www.tamrac.com/products/pro12/ Internal 15" W x 7" D x 8 1/4" H
http://www.tamrac.com/products/superpro19/ Internal 14" W x 6 1/4" D x 11" H
Look for a back pack that put the weight on the hip with a padded belt.

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