A block heater will defintely help, above the 49th parallel we consider heat "life support" for our engines 3 to 5 months a year. But at 30 degrees it should start with glow plugs if the compression is good. Tazza has a thread or two about checking you gp's
Worst case, glow plugs elements are burnt out they are not getting power from the key. Your volt meter should drop when activated. Test the bar conecting the plugs to see its getting power.
Then unhook the plugs from the bar, hook you test light ground clip to the battery + and probe each glow plug to see if the light can get a ground though it, no ground = dead plug.
Also they do "wear out" and if the budget allows and the ole girl has some long hours on her, then a whole new from your favourite auto parts store would be a good choice.
You can remove them and power them up, they should glow at the tip and work its way back, if they have no tip, they are past do for changing.
Also if you a fan of 15/40 or some other thick as tar motor oil you may want to reconsider for the winter months. My LS 160 thinks 5/30 is to thick and lives on a year round supply of 0-40 now
Regards
Ken
Ken