Help me find a backpack for my massage kit.

Just to clarify - the bag itself needs to be at least 110cm x 40cm?

I recently got a http://www.amazon.com/exec/obidos/ASIN/B008BZLV22/metafilter-20/ref=nosim/ and it is awesome. It's a solidly constructed, well-organized duffel that is also a rolling suitcase and also a backpack. I can't recommend it enough. It has an expansion zipper, and compression straps to cinch it down. In backpack mode it's remarkably comfortable (not as good a real backpack of similar size of course, but much better than just putting your arms through the straps of a regular duffel) and as a rolling suitcase it also works excellently. I haven't had it for long but as I mentioned before the construction seems excellent; it's heavy-duty nylon with good zippers, sturdy stitching, metal wheels, and reinforcements/rivets where needed. It's even remarkably light! I really can't find any fault with it. My version may be a little bit small for you but http://www.amazon.com/exec/obidos/ASIN/B008NUMHL4/metafilter-20/ref=nosim/ that might suit you. The big one has a capacity of 131 liters and dimensions of 81 x 32 x 32 centimeters in collapsed mode. If that's still too small and you don't care about backpack straps, they make a http://www.amazon.com/exec/obidos/ASIN/B004C0XHL8/metafilter-20/ref=nosim/ that's a size larger and appears to be essentially the same idea except minus the backpack straps and, well, bigger. It's also a good deal cheaper, which is always a bonus.

The thing that immediately comes to mind is a hockey bag. Big, sturdy, and comes in wheeled and backpack styles.

Try http://www.timbuk2.com/tb2/shop/category/duffel-travel-bags. There are lots of great styles, and I can vouch for how well they're made - the messenger bag I have lasted longer than my marriage.

I would be looking at dry bags. http://www.nrs.com/product/2925/nrs-system-5-dry-bag?avad=25261_b5fd1329, at 42",but not quite. If you look at the photo of the model on that page you can see why it's hard to find packs this size - it hangs down far enough to impede walking. Dry bags can be tough to load and awkward to pack (granted I used mine to carry a heavy wood djembe drum) but man is your stuff dry. Also would be better to lash to rack on bike due to compression straps. Generally dry bags are rugged and survive falls well. Duffel bags are really much easier to pack and you will appreciate this after a while. Rummaging around at the bottom of a 115L+ pack is no fun. http://www.nrs.com/product/55414.02/watershed-mississippi-dry-duffel that will (just) clear your futon. You can go to canoe, kayak, or boat suppliers in your area to inquire about a slightly larger size.

Thanks for the suggestions so far! @HuronBob: some of the Army duffels look great! I'll browse around for their larger sizes. Perhaps I could ask a friend to add a few extra inches to http://www.armysurplusworld.com/product.asp?ProductID=17941 for example. @barnone: the main thing is the futon, which is 100x40cm rolled up. If all else fails I could -theoretically- carry my other things in a seperate bag, but this would be a pain when biking and walking. @padraigin and @crazycanuck: oh! I hadn't thought of those sports. Great! The 42" dry bag might actually be big enough.

Have you ever considered investigating panniers or racks that might hold it properly? You could put it in one of the long dry bags, then have it strapped diagonally on the back of your bike? Or is that just a crazy idea? Or what about a small trailer? It depends on how much of a pain the backpack is, but there are other ways of transporting such bulky items.

Here's http://www.futonpacifika.co.uk/proddetail.php?prod=202 - designed for massage futon mattresses. Maybe they'd be able to make one with shoulder straps in addition?

And here's ahttp://www.amazon.com/exec/obidos/ASIN/B0051DV35W/metafilter-20/ref=nosim/. You could have someone sew on reinforced backpack straps. Final thought: snowboard travel cases are very long and some have room for multiple boards. There are also wakeboard bags. Most just have one shoulder strap but I bet there are models with backpack straps!