My preference for hauling Kayaks, is what Buzzcut1 has shown and it works really well.
The mantra I share and use often; "Is the easier you have something stored or carried, the more you will use it." Like I changed my Mountain Bike set up from a fork mounted carrier, to a process, where my Mnt Bike is held on by one single shock cord, with all rims/tires mounted. Makes it easy to grab and use, whenever the urge hits. It takes longer to put on my cleat shoes than it does for grabbing the bike.
I carry my 14' Wilderness Tsunami Backcountry Kayak and my Liquid Logic 150 white water kayak inside my Motorcycle trailer, along with 2 motorcycles and a large battery bank and Solar Array. So the suggestion of using a trailer is perfect for me, as I can use it for other purposes, as well. My Kayaks are simple to pull out, to use, too. They are both held to the wall, of the trailer, with two Tie Down Ratchet straps. Easy and quick to pull either one of them out, plus I don't have to climb up on the roof of my TC.
Some carry Fold a Boat to the side of their Truck Campers, too. I really like those suitcase Kayaks too. There is a new movement to use these and inflatables to access more wilderness areas by carrying these on your back, folded up.
Whazoo has a Rack system for his pop up camper, where the end of the cross bar can be pulled out and the tip of the Kayak set on it, allowing one to Teeter Totter the other end up. Saving one from supporting the entire weight to get the kayak up onto the roof.
Since I carry my Mnt Bike on my Adventure Motorcycle, I want to get a set up to trailer my Kayak behind it too. That will open up even more possibilities for me with my Kayak/s.
Any way you go about it, having your Kayak right there within arm's reach is a great way to compliment using your Truck Camper. I never go anywhere without my kayaks, recently getting them wet in the Cowlitz and Rogue River, as well as the bay off Whidbey Island.
Have fun, as there are many ways to accomplish what you would like to do.
b