No easy way around it. Ever time I wrap up the cord in colder weather my first comments are....I hate 50A. But then come mid summer in the Mid Atlantic heat and humidity and its a nice cool 70F and low humidity indoors I am thankful for having 50A.
I found there are two ways to coil it up that works well. One is to get it set out in a straight line and starting with the outlet end just slowly coil it. Another method that has worked for me in colder weather is figure 8s in about the size of the final coil, once the 8 is done I can fold one side over to the other and tie it.
I have consider a proper sized tub where I could stack the main cord and my extension in using just the figure 8 method, but I have not found one with strong enough sides yet.