how long do the block heaters usually last on these trucks? its been really cold here lattelly and iam retired , dont drive the truck too much till spring time in the past when i was working i usually pluged in before bed and nice and warm in morn. but lattely i,ve been leavinn it pluged in all the time, but iam worried it might crap out on me, think ill have to leave it pluged in for mabye 1 more week, think any harm? i know about the power bill ill have but thats ok.