Best Way To Keep Sub-Urine Warm

Here I go again!
All the info I gather from this site is so educational..
I'd like to get some feedback on experiences with subbing urine for u/a..
Whats the best way to warm the bottle? Lets say test may be a surprise and you have to pack the bottle on you all day ..Will body temp be ok or hand warmer better? From my experience and practice runs the hand warmer gets its a pretty hot.Hotter than needed..I have a strap with a pouch that wraps around your upper thigh next to the crotch..Would a person be safe without the hand warmer? Would anyone like to share their personal experiences..especially having to wait in the waiting area and office for 1-2 hrs..anyone??

any advice?? this will make a good thread "strictly about warming methods" from our personal experiences..the do's and dont's for all of us pot smokers who have to deal with the stress of urine analysis..

Hand warmers work pretty good for a substitute bottle but sometimes they make the urine a bit too hot..a good quick cooling down method tip would help a lot as well..ive heard people stashing bottle under crotch to keep it at body temp but I have 2 buddies who recently failed u/a because the temp dropped too quickly..also some labs wait 4 minutes before taking the temp because artificial heating supposedly cools at a faster rate..again any feedback from personal experiences would be greatly appreciated..