Reminds me of an afternoon at the gliding club I used to help run in my spare time many moons ago. One of my friends had an old pre-war German 2-seat glider called a DFS Kranich. I took one of our solo pilots flying in it and it was such a hot day that we were flying it with the canopy off.
We got underneath such a cloud and we were climbing like a train and the bottom was getting blacker and blacker. I suggested to Charlie that we moved off out of the way but it was too late. Charlie was used to flying gliders with powerful speed limiting airbrakes and not plywood balloons with tiny ineffective spoilers.
I took control as we got swallowed up in the blackness and finally emerged out of the side of the cloud fortunately with the wings level and still the right way up. We were both very wet.
So, unless you really intend to go into the cloud with a full set of working instruments, I would suggest going round the outside by a sensible margin.