In the video interview of Kore Flatmo, he mentions the use of a numbing agent in the place of regular vaseline. Could have been a lidocaine blend. Worth listening to his thoughts.
I just got my chest done last week. I was in from out of town and keen to get it done in one sitting. I ate a good lunch prior and snacked on a p.b. sandwich during short breaks. Kind of sucked towards the end but got it done in about 4 hours. I agree with the tensing up, breathing worked for the first portion, but I got more tense as we progressed.
I'm not sure what the ribs are like compared to the chest, probably worse?