I'm assuming that by "roof not an option" you mean the exterior roof.
I didn't buy a 'product' as such. In our Excursion, Suburbans, Cherokee, and Volvos I suspended clothes rods from the stock hooks near the roof. The clothes rods are encapsulated in foam insulation tubes, and I wound an elastic cord the length of the rear one.
The tips go forward and the reels prevent the rods from slipping forward. I use the elastic cord to retain the butt ends in place.
I'm not sure what I'll do in the Dakota we now have. Unless I open both the window in the truck cab and the forward window in the camper shell, I can't suspend a rod from the roof area. I do have a couple of carryiing cases that let me leave the rod partially assembled, i.e. leave the reel on, the line through the ferrules, but separate the rod at a convenient joint and insert the now-two-piece rod into the case.
If I'm just moving from one spot on a stream to another, the exterior magnetic mounts I have work fine, but I wouldn't want to drive at speed with the rods outside.
Years ago, I used large-diameter PVC (held three assembled rods/reels) mounted on the roof of the vehicle. This worked beautifully and was really great protection for the rods. I may try something like that again on this Dakota, but I'll try to find thinner-walled pipe.
BTW, I'm describing fly-rods that can be broken down into two, three, even four pieces.
Allen R