So yesterday marked the first time I became frustrated to the point of actually slamming glass!  =)

For the last three days I have been in great distress over what seems to me a total inability to properly form bends.  Then often when I did succeed in a simple doubleback, the bend would crack after about 30 minutes.  

I'm now thinking it's due to a cold propane tank, is that even a thing?  Mind you, I'm in Central Florida, so cold here is like 40-50, but that's a vast difference to the usuall 90+ summer temps. 

I've ordered one of those heat wrap things to go around the tank, and should be here in a couple of days.  But Holy Hell it's been a nightmare!

Oh that sounds so frustrating! I use natural gas and I don't know if cold propane is a thing or not, but maybe someone here who uses propane can weigh in. Your problems could be related to the glass itself. What type of glass is it? I know there have been issues with snow white and green recently. And I've problems with blue cracking minutes or hours after a splice has cooled. Flame annealing a bend can help with the cracking sometimes.  

This is most likely not a propane problem.  Propane is a liquid at normal room temperature ranges while under pressure in the tank.  As you open a valve and the pressure decreases, more liquid boils off inside the tank to replace the pressure lost as you withdraw the gas.  The boiling point of Propane at standard atmospheric pressure is -41F.  This means that you can have liquid propane in an open cup if the temperature of the space is colder than negative 41.  I have demonstrated this on a 50 below day in Fairbanks!   Obviously your Florida location doesn't get that cold.  So you should have ample boil off inside the tank, and so long as there is not an excessive flow rate that could cause rapid cooling inside of the regulator and freeze it up, there should be no problem.  A tank heater is useful in winter when the temps are below freezing, because they help maintain the flow rate efficiency, but again, this is not likely your difficulty.   I use propane exclusively, both in Alaska for 30 years and in my new location in Minnesota.   If your tank/regulator is freezing up, you'll see it as not getting enough flow to maintain the fire at the levels you set--and as discussed above, it must be very cold for that to happen.  (the only caveat being if there is water vapor inside of the regulator or tank--it should never happen, but it is a possibility in very humid places and with random sources for filling)

If you were able to get enough flow to set your flames as you'd want them for bending, then you are getting enough gas and airflow and so a cold flame is not the trouble here.

Most likely, you are dealing with either difficult glass, as Eve has suggested (that blue was a terrible bad phosphor that was not compatible with the base glass and caused a lot of trouble) or you may have a cold table surface that is wicking heat away from your glass too quickly when you put it on the pattern to bend.  Try placing a space heater under the table surface.  You should also avoid leaving anything to cool on the table.  As soon as practical, get it up off of the pattern and let it cool in the air.  This will avoid uneven cooling.  Also keep in mind that the sticks of glass in the boxes may be rather cool (especially if the room got cold overnight) and need more time in the fires to warm up enough to be workable.

A cool room is not a show stopper, in fact, I can't stand a hot room!   I aim to keep my studio space between 58 and 70 degrees no matter what I am doing and if it gets up to 75 I avoid doing much and if it hits 80 or above, I do not work. 

As luck would have it, the glass I'm trying to bend is FMS BL55 Blue.  

I have installed the tank warmer, and while it seems to keep the fires more consistent, and I've been able to turn down the flow quite a bit, the glass still cracks.  

Ignoring the fact that it's likely made worse or entirely due to the bad batch of blue phosphor, I'm thinking it's as you suggest, the glass and bending table both being colder than usual.  Normal for my shop most of the year would be 89-95, so a cool pleasant day would be 85.  We've been having night temps around 38-45, then up to 65-75 daytime, so the box of glass remains very noticeably cold.

I switched from using the screen on a paper pattern to using a cloth pattern, and it seemed to help a little, but warming up the table with a space heater is a simple trick I hadn't considered.  I'll do that right now.

Maybe I'll just stop with this glass and come back to it when the hot weather returns.