Specifically, I'm trying to come up with a system to carry two canoes (a tandem Souris River 17 and a solo Wenonah Prism) on a 2014 Subaru Wagon with factory installed rails.

The Thule & Yakima websites are very frustrating & seem to have no offerings with crossbars long enough to do the job.  Perhaps they have a safety concern carrying two canoes on a roof?  Their websites are clearly leaning heavily to accommodating kayaks these days, it seems.

Anyway, I may be down to building a home system using 2 X 4's - which is fine, I guess - but I would have thought somebody would have sold a standard package that would do the trick... like a set of 4 towers with options on cross bar lengths to meet specific needs.

Any ideas or suggestions where to look?  Hard water season has arrived in MN so "time" is a luxury I have....

Jimbo   

I have something much like ST is suggesting except the whole unit is integral and ready to use with telescoping side bars. Works supremely well IMO.

I think I got mine from Piragis some 10 years ago and picked up the suction cup front rack as well as another rack which mounts into my trucks receiver hitch.......slick set up. I know the entire shebang was around $200 but now they want $180 per unit (ouch). Lately I have just been using the front suction cup rack and using some foam blocks for the rear. Ropes via truckers hitch secure the boat to the vehicle in addition to being secured to the rack. Good set up which is easily removable.......another plus up

Jimbo, I'm guessing you have the Outback not the Forester??
The Forester should work OK with the longest bars from Yakima and some universal Yakima towers. You can get a receiver hitch for the front of the car too, for an RV tow behind application. This is the same Dry Dock Puckster mentioned, but on the front instead of the rear. This will give you a nice spread front to back for longer boats.  Just another option. There is a legal limit to how much overhang you have out the back. Plus it's nice to be able to open a rear hatch.

The Outback,,I've seen guys remove some of the plastic covering of the racks to attach to hardware underneath the plastic.

Take pictures and tell me how it works.

Yakima also has a "Landing Pad???" that you drill and mount to bare roofs. I wonder if any of the factory rack mounting holes would match up with the landing pad? It would mean completely removing the factory racks and mounting the landing pads.

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I always start my car buying with the "How will it carry boats question"? Racing boats are more sensitive to high winds on highways than rec boats. It's not looking good for newer vehicles, and trucks are getting stupid expensive. 

You may want to try looking at Malone " (You need to Login or Register to view media files and links)" My son got a set of steel bars from them that are plenty long enough. You may not be able to get the aerodynamic style bars in a lenght long enough for 2 canoes.

Lots of great observations & ideas, guys.  Thanks!

Magic, I don't have the car in my possession yet (it's getting underside weather protection & Scotchgarding on its upholstery this week), so I can't measure that open distance on the railing.  Nevertheless, as mechanically-"disinclined" as I am, I do see your point.  To insert towers in the slots provided probably does not offer me the spacing I would require.

Rather, the SteelTop™ MPG200 Series Steel Rectangular Profile Cross Rail System from Malone that Fallguy has suggested might actually do the trick... IF the towers mount around the outsides of the rails vs. in the slots OR having to go completely around the rails.  The picture ( (You need to Login or Register to view media files and links) ) is somewhat unclear about this.  If these towers must "wrap" the rail, I guess I would need to remove factory installed plastic (not necessarily something I want to do on a new car).  If they mount "outside" of the rails somehow (like a clamp), it would allow adequate spacing of cross bars.  Of course, I'd need cross bars at least 78 inches in length to go along with that system.

My guess is that system needs to wrap the rail somehow, which means getting under the plastic as Jim J says.  By the way, the car IS an Outback, not a Forester.  I also appreciate Jim J's sentiment, "I always start my car buying with the "How will it carry boats question?"  In this case, my other needs for this particular car outweighed that consideration... but the thought was indeed on my mind.

It just seemed to me that there should be SOME system designed to take advantage of factory installed rails.

Of course, there is always THIS solution: (You need to Login or Register to view media files and links) .  The Outback can tow 2700 lbs; the trailer runs 2200 lbs.  With packs & canoes, I should still be OK, even as heavy as I pack.   It's pretty flat between the Twin Cities & North Country (famous last words), right?

Thanks for the ideas, guys!

Jimbo