Canon has since a long time soft cases available for the super telephoto lenses, called "Soft Lens Case". I got the Soft Lens Case M II for the EF 200-400mm f/4L from ebay back in 2014. Article "S.CASE-M2", 9390B002 for about $200. The case has been available in four sizes, S II, M II, L II and LL II for lenses like the EF 200mm f/2L to the EF 800mm f/5.6L.