You can use the tow mode all the time even when not towing. All it does hold the lower gears longer so you can get up to speed. Towing your camper two mode is a great. It is not needed for light weight towing and your camper doesn't meet the manual stated 75%. Give it a try and see if you like it.
Cruise control and towing is a personal preference and the manual says not to but that is do to safety reasons. I use cruise while towing and the only thing it does for me is give me better mpg. The tranny will shift as needed with or without cruise on.
80% is a good rule. Another good rule is trailer length for truck wheelbase. Lots of info on the Internet about that. Most 1/2 tons trucks are maxed out in length at 27ft but that is per X amount of weight. There are few guys pulling some long travel trailers with their Titans. It will do it but how safe is it, I don't know.
Good info here
http://www.rvtowingtips.com/how-long.htm