Well it seems everyone here isn't answering your question...
You probably don't need a cover letter when you fax. I called all of my schools today and asked "do you accept faxed or scanned/emailed DAT score reports" and if yes, then "do I need a cover letter?" They all said no, and Case said it's optional, but not really needed. So, only one sheet per school that allows you to fax in scores. Also ask for their fax number as they may have multiple machines. Write down all of your fax numbers, take them to an office/printing store and say "I need this sheet of paper faxed to these numbers, thanks!" They will then fax it for you, and give you a confirmation of delivery when it arrives at the school's fax machine.
To make it even easier for you, these schools accept faxed score reports: Case, Columbia, UPenn (accepts emailed ones too), Baylor, NYU, and Tufts.
These schools do not accept faxes: Pacific, UCSF, Houston, and UTHSCSA
Hope that helps. On the other hand, I will have to agree with everyone else and say that Google could've easily answered questions on faxing and faxing etiquette in general, I don't think SDN is your only source for info 😉