I see posts like this in the Toy Hauler forum fairly frequently. If you search there you'll find some recent pictures of kayak storage racks that people had fabricated.
You might consider clicking Notify Moderator and asking to have this topic moved to the Toy Hauler forum.
But to answer your question, yes, it's pretty common.
How long are your kayaks? As you shop for fifth wheel toy haulers you'll see garage models and open floor plans. The garage units typically have either 10' or 12' garages. If you need more room than that you'll have to go with an open floor plan.