i feel your pain! i have a 300 turbo that would NOT start when the temp went below approx 20 deg F. i installed a block heater (the plug and wiring was already in place) and plug her in when really cold temps are present. that solved all my cold starting problems.
when the prob 1st showed, i went to my trusted mech, and he said: "your bought yourself one of those "summer" diesels."
anyway... the problem is mostly related to compression. i could crank forever with a great battery to no avail. if the compression is not high enough, it will NOT generate enough heat to fire when the block is REALLY COLD. it also helps to add a D-fuel additive such as redline during the winter.
get a heater installed, plug it in, and sleep well KNOWING that your diesel will fire instantly whenever you desire to go!
i seem to remember paying about $35 for the heater installed.
or... i was in key largo last week, and im sure your diesel would fire any day in a similar climate!