I haven't posted in quite some time. I love my TC, but in two years I will replace at least the truck. (Because I am at the polar opposite of mechanically inclined!) I understand the weight restrict...
Not sure if I am understanding the question. If you are looking at a new truck the dimensions are easily found online. If you are keeping your old camper measure how much extends off the back off the truck and add that to the trucks length. That should get you pretty close. The actual overall length may be a few inches shorter for the bumper which would be included in manufacturers length.