Wayne,
I don't think you would have any problem. Heck how many people here have loaded 400# in the very rear of their truck and driven with them without any problems. With your truck I wouldn't see that the truck would even squat at all. I think the main reason for the warnings is with heavier trailers and the hitch in the rear position is it could cause a lot of sway. Your light trailer is not going to cause any sway. Also it might be a braking problem with a heaver trailer that the hitch is not built for the force pushing forward on the locking device. Where the slider in the front/travel position it is locked into the front/beefer portion of the hitch but again I don't know if with your trailer if this is a concern.
I have seen your posts on the TC forum when I carried a TCer so I know you are inventive so look for a way to make a brace to make sure that the slider is locked so it can't slide forward in an emergency braking condition and I wouldn't see any problem.
Butch