I have a new challenge to solve...I am the proud owner of a 2 yr old Munsterlander Setter dog (adopted) who will add another 60 pounds to my already overloaded Poke boat kayak.  I've researched some plastic pods, made to pull behind kayaks, which seem doable but are also heavy compared to carry capacity.  So now I have ordered an Intex floating cooler (for tubing) which should carry 60 pounds and will try towing THAT with gear in it.  Dog will have to be in kayak with me.
It looks squarish and not too streamlined for towing so I plan to make a silicone-coated fabric "sled" to pull it on through the water which should help in making it slippery and I'll make a contoured, pointed front end on the "sled" to help make it more streamlined.
  Remains to be seen how this will work. 
Any other suggestions out there???

I do need a bigger boat...but looks like I'll be carrying something around 55 pounds if I got one.  I can do it...but not sure I want to do it.  I expect I'll have to stay in camp on really windy days, no matter what; since I can't be sure the dog will stay put until he is more used to the boat and perhaps settled down a bit more.  He's going to be the type to want to dive out of the boat after ducks, etc.  It remains to be seen if I can successfully train him not to jump out on a whim.

I am worried that any type canoe will be quite a bit more unstable than the Poke boat.  In the past I have taken one of our other 60 pound dogs out paddling in the Poke boat and she does very well...stays down and keeps her weight in the middle of the kayak.

A few years ago I had to do a trip where I paddled one poke boat and pulled a cooler and other gear in a second poke boat.  That was not too difficult to do although I did not have to do it against any strong headwinds.  I was in a fairly strong side-wind which drifted the "trailer" downwind from me; I didn't have any fancy towing rope plan to oppose that.  I see one of the pods I researched had a somewhat rigid towing plan made of PVC pipe to hold the boats apart and in line.

IC: If only you could pull on both ends of that poke boat and turn it into a vagabond  (You need to Login or Register to view media files and links)

Towing anything by paddle will be a job.  Anything less streamlined than a canoe will be a PITA.  But if you insist, here's how to connect the towed object.  (This comes from having towed a loaded solo canoe behind a tandem some years ago.)

This arrangement will prevent the towed craft from slewing sideways badly and eliminate the bumping involved in rope towing.

Don't use a rope.  Use a curved stick about 6 feet long; it should have at least 2-3 inches of curvature.  The stick needs to be arched to clear the deck plates of the two canoes.  If you aren't using canoes, you might be able to use a straight stick.  Attach one end to the stern of the tow craft and the other end to the bow of the towed craft.  If the stick is curved, the arch, should be upward, and the method of attachment should keep it that way.

A much better approach is to use the proper craft so you don't have to tow.  If you're concerned that a canoe won't be stable enough, do the following:

1.  Learn to paddle a canoe.
2.  Get a canoe with a shallow-arch hull and enough capacity to carry what you want.

I'm still going to give the towable cooler raft a try since it is on order and only cost around $30.00.  I know it is not going to be fun to pull anything but shouldn't be too hard except when the wind is against me. 
Meanwhile I am on the hunt for a Vagabond Poke boat.  Found a fairly extensive forum for used Poke boats on "Mykayakingbuddies" web site and might have some luck there.  Anyone know someone with a Vagabond they want to get rid of?  I have several of the 12' Poke boats and could trade or sell one or two if someone wanted to scale down.