I have a Lowe Pro Passport sling (shoulderbag) that takes my Yashica 124G, a Zeiss Ikonta 6X6 folder, Sekonic meter with plenty of room left for film. As I recall the SQA aint much bigger than a TLR and it should fit into the passport sling (though its not a backpack). I have my Pentax 6X7 (45mm + 90mm + tubes) in an old lowepro Street & Field sytem backpack (dont remember the name) with a compartment for otherstuff on top and photoequipment in the bottom. It will easily take a bronica + three lenses. Should be able to find one used.
Best regards