My 2 cents.
If your going to have one built...see if there is some way with all the modern tech the nose of the camper can rest on the roof with some sort of gym floor foam type material between the roof and the camper. 2) Make the nose section just like a chinook chalet minus the windows ( no matter what you do the windows will leak ). 3) FWD / PHX campers do not bolt to the back of the cab...only the bed rails where the original fiber glass top rests. Makes for wind noise and leakage. Chalets bolted to the back of the cab and the rails so the fit was great and no noise and or leaks. The rounded nose is the key in my opinion. Having owned both on K5's and driving the chinook version from colorado to canada for work the chalet is aero and actually delivered pretty good fuel economy while the the fwd/phx/hallmarks are like a brick. You will feel a difference between the two. Also for general knowledge...a chinook chalet requires a upgrade to 3/4 ton axles so you can get a heavier sidewall tire on as the 15 inch relm is limited. The extra capability of the 16" up tires sidewall makes a Huge difference in handling.
I don't own one anymore although i now have the K5/Jimmy i have always wanted built i just lack the camper. Never fails...
DW