I use them almost exclusively these days. I have ione that is cut down to about the width of a normal mat, with a leather bootlace tied in one end. Simoply roll it up, tie the lace around it and stick it to the outside of the pack. If you risk getting wet simply place them inside something waterproof (I use a black bin liner inside a thin canvas sack, but you can go gucci here). They are about as heavy and large as a full size closed cell foam mat, but they have something the clesed cell foam does not; "feeling".
IOW; yes, I am irrational, but I like my irrationality.
A lot warmer and ever so slightly softer than lying on concrete, they shed hair and are huge to pack.
Nice if on top of a foam mat and you have a car to carry them. I gave 2 away after spending a warm, but very uncomfortable night on them. I'd go with sheepskins, nearly as warm, easier to pack and dont moult hair everywhere.