The sliding hitch should prevent any problem of hitting the cab with the trailer--assuming it is automatic, or, you remember to activate it. Using a headache rack will only reduce clearance and if you hit it with the fiver, it will be forced into the cab anyway.
Good luck, welcome to the forum.
2016 Tiffin 40 QBH
2015 38RSSA, traded
2005 TK3 #1869, 10 yrs of memories,
2017 F450 KR--one more Ford is it
2009 F450 4x4-died; 2010 F450-retired