If the ONLY thing you are going to use your truck for is a Lance camper, you can have your RV dealer install the Lance specific receptacle in your bed. If you want more flexibility, you can install a standard 7 pin plug and then just make a pigtail adapter that converts the 7 pin into the Lance plug spec using a wire similar to the etrailer link supplied a few posts above. My local RV shop fabricated up one of these for me and IIRC he charged ~100 bucks for parts and labor to fabricate/splice. Worked fantastic.
I did this with my Lance on my F350. I can use one single plugin at the rear of my wheel well and plug in a 5th wheel, gooseneck, Lance, or any other brand camper. I'm glad I went this route as I eventually sold my Lance and bought a Host Everest so the Lance receptacle would have no longer been applicable to my camper as the Host (like most every other camper) uses a standard 7 pin plug.