Using the M on the Ford F150

M I believe stand's for 'manual' which is the up and down arrows on you shifting lever. depend on you knowledge, if you feel comfortable with shifting for yourself and depending on the length of the hill most loads like a camper have their own breaks that are controlled by a box in the cab of the truck unless the truck came factory with it bilt in which idk where it would be located. However back the the actual driving. A 7% grade you should be fine using your breaks and keeping the transmission in tow/haul mode which is normally in the end of the shift lever

Read your owners manual! There may be a tow/haul mode which you should use if you have it. I would most definitely gear down on a 7% grade.

For your reference a 7% grade is considered quite steep.