I've missed too many shots because of caps. Use them only for transporting in the bag or the pocket, and only slip-on caps (Heliar 15mm, Color Skopar 21mm and 28mm). With other lenses, I have a hood - or nothing. Even when used with the M6 - the chance to burn the cloth shutter is close to zero. First I rarely use f8 or higher, second I don't put it somewhere with the lens directed to the sun, and third when I walk toward the bright sun I keep the lens down. Worked well so far.
I noticed most pro photogs don't use caps outside the camera bags, too, and are not worried to clean a $3k lens with their shirt. But I wouldn't try that with a 1950's Leitz lens...
Didier