I’ve had racks on three capped Toyota pickups, and there are a number of considerations to bear in mind or design for. Foremost to my mind is how the canoe (or canoes*) fit on the rack.
With racks mounted to the cap, at least with a low-rise cap at the same level as the cab roof, there may be issues with the bow of the canoe resting on the cab roof. One solution is to put the canoe on positioned far forward, so the bow tip is out past the windshield.
That solution is a no-go for me. For one thing I want the canoe more centered on the racks, with an equal amount of hull out past each rack, and for another I load our heavy canoes by sliding them on from the back of the truck, and don’t want the bow scraping its way across the cab roof.
I’ve had racks on (or around) two low-rise caps. On one I built “risers” (which also added length to the crossbars*) for both racks, so the bow was elevated above the cab, and I could still slide canoes on from the back. On the other low-rise cap I used heavy duty construction racks that cantilevered off metal plates bolted to the bed rails, those racks went around and over the cap, never actually touching it, an could be height adjusted.
Kinda like these, but designed to wrap around the outside the cap.
https://www.weatherguard.com/products/truck-tool-boxes-equipment/truck-racks/TruckRack/TR801-A
My current truck cap is a mid-rise. I did some measuring and testing to see how high I needed to go for the bow to clear the cab roof using the height of Thule racks and feet I already owned; a mid-rise cap was sufficient.
PB140063 by
Mike McCrea, on Flickr
Another possibility, about which paddlers have differing opinions, is to mount one rack on the cap and one on the cab roof. Some folks believe that any twist between cab and bed will torque the hull, and I can
maybe see that damaging the hull/deck seam with composite sea kayaks
But, unless you are rock hopping in your truck, I kind of doubt that is an issue; the back wall of the cab and front wall of the bed on my Tacoma are less than 1” apart. If that gap twisted and flexed enough to harm a canoe I think I’d see sheet metal damage.
With a cap and racks on a Tacoma you will have one of the best canoe tripping vehicles around, and can start tricking out the bed as a live-aboard.
PA010020 by
Mike McCrea, on Flickr
Gear for two guys on a 7 week trip. All of the gear is webbing strapped to tie downs so nothing moves, even on bumpy back roads.
P4151833 by
Mike McCrea, on Flickr
Note: I don’t drink Tequila. Or Franzia.
So nice back there I think I’ll have a rest and get out of the sun.
P4191869 by
Mike McCrea, on Flickr
*Last bit of (unsolicited) rack advice. If your roof rack crossbars are only long enough to carry one boat you are plumb useless when cross loading boats on a shuttle. Get long enough crossbars to carry two canoes. I’m operate on the theory that if my crossbars don’t stick out past my wide view mirrors I’m street legal, and unlikely to catch a signpost or whack a pedestrian.
If that rack length is a problem get bigger mirrors J