Tom, (this is an old thread?!)...we have been using the p-bote for several years now...it is terrific.
We have a 14' and use an 8hp 2 st (yes we can still use those around here) so laying motor down in any orientation is ok (another bonus of 2 st's) the 8 hp is more than adequate for the 14' with 3 + 70# lab.
We occasionlay put 5 in the boat when my Folks come to visit up at the lake...it is till comfortable and quite stable.
We sometimes carry 2 tandem kayaks and the p-bote on the roof. Truck is much like the Suburban...as a matter of fact, we use some hitch/Thule/etc components from when we had Suburbans so you should have no trouble. If you look closely, you'll see the p-bote under the kayak.
We have travelled thousands of miles like this.
*Life is Good-Camping all around the Continent*
*Good people drink good beer-Hunter S Thompson*