I think they are seldom prewired, my manufacturer said as much to me when I ask the question.
I do not have the same coach but did have the same situation. I found a fuse panel with extra space and male connectors under the dash against the fire wall. I just installed a fuse an connected the hot to the fuse panel with a female connector and found a ground.
And yes it was not an easy crawl uder there to connect everything but I lived to tell about it.
Anywhere you have an extra fuse location would do. Just need a longer wire.
I installed a CB which had the receiver under the dash and the microphone held all the dials and buttons. Very clean install.
I do all my own stunts
03 Dolphin LX 6355, Workhorse W22, 8.1 vortec, 04 CR-V, Blue Ox, Brake Pro----Norm, Barb and
Doc(He's a PhD)