Questioncan I put a double din in a 99 F150?
AnswerWell, nothing is impossible. But, some things are more difficult than others. I don't think this dash is made for it by you may be able to fit it with some clever ingenuity.
http://installdr.com/InstallDocs/FLM/PDF/356017.pdf
The above has some photos that show the details of installation that might help you determine how to proceed on a custom basis.
http://www.installer.com/kits/
Above has some double din install kits for various Ford vehicles, but I didn't see one for the F 150. You might contact them and see if the can recommend one of their brackets.
Best wishes,
C