Penis latex sheath-How to get it on !

I have a new penis latex sheath which has a combined pouch for the balls and a drain tube at the very end,when worn they are supposed to be very enjoyable,the problem is try as I have I cannot get the thing onto myself ? placing the penis shaft into the sheath first then pulling the ball portion open is still impossible.

Can I really strecth the latex pouch first to attempt to expand it or is there another way to get this on ? any help with this would be appreciated.

Roll it on like a condom if you can then you need to stretch the ball sack to fit