The 70-200mm f2.8 fits well in the pouch with the lens hood in the working position. Since the 100-400mm and the 70-200mm f2.8 are similar in length, stacking the converters will add about three inches. If you keep the hood off or reversed, it will most likely fit.
Thanks again ED, I need to make sure before I buy. We do a lot of Bald eagle photography here on the Mississippi River in mid winter and it is a pain in the but to keep assembling the three parts if I need the length. So would like to put them together at home then just add the body at the lock and dam sights.
Total length of lens and both converters is 12" so it may work. What is the length inside the pouch?