One great piece of advice I got for carrying a rifle and shotgun to Africa last year was to purchase a heavy plastic lockable golf club case.

They are darn tough, roll-away, have enough room to put a bunch of other gear in (and yes, you'll probably get charged an overweight fee). But they look (obviously) like a golf case, have room easily for four long guns, and probably only cost half of what a bonafide firearms case costs.