You say you "have a little trouble starting" but don't mention exactly what the problem is. If the engine catches and just has a real rough time idling or stalls, then use the glow plugs again after it starts. When it drops below 20F or so, I do this; I put the throttle to about 1/4 and turn the key and wait for the glow plug light to go out and then crank it. As soon as it catches and starts, I release the key to the "on" position and then turn it to the glow plug position again and hold it there until the idle is smoother (usually 2 or 3 seconds). Since the engine is running, this is not draining your battery at all as it would if you just cycled the glow plugs twice before starting.
If the problem is that it doesn't catch, then either your fuel is slightly gelled, the fuel filter is clogged, your not given it enough throttle or your glow plugs are not working properly. A block heater really just heats the oil in the pan and makes cranking a ton easier since the oil is warm and thinner and a lower radiator hose heater works good at heating the coolant and circulating it by convection but I don't beleive either is necessary until well below 0f temps in these little engines. A full size diesel truck is another story.
