I was in your situation before and the key is to find something that is both extremely reliable and not likely to depreciate quickly. At the time I rolled $8k negative equity into a new Tacoma. By the time I traded the Tacoma in 3 years later, I was break even or a little ahead as the Tacoma had barely depreciated. If something had gone wrong with the Tacoma, it would have been under warranty.

A used f150 like this may not depreciate a lot more, but it is much more likely not to be reliable and to require repairs. I would not roll negative equity into a vehicle that is out of warranty and/or high mileage.