Lance owner here. Just went through this. Yes, Lance plug is different and the only place your going to find the appropriate plug for your truck is a dealer or something like Ebay. Other dealers don't carry them. There is a small chance your new to you camper will come with one as they are supplied with every Lance camper. But, if not, contact a Lance dealer and either buy the plug for the truck and wire it in appropriately or get the 8' Lance extension which comes with the Lance plug on one end and bare wires on the other. You can then add a 7way plug to the bare wire end and run it to the 7way on your truck at the rear hitch location. This will get you using your camper and later decide if you want to permanently wire in the Lance plug in the bed of your truck.
P.S. The reason the Lance plug is different is that 8 gauge wire is used to power the possible 12 volt fridge in the Lance. If your not going to use the 12 volt feature of the fridge then you don't need to worry about the 8 gauge wire requirement. The above instructions I gave you assume your not running the fridge on 12 volt.