John, I'll Weigh In On The Watertender..
..I have one that I tow with my L40.5. It has a 3.3 Mercury OB that is the same as Nisson or Tohatsu. I got cushions custom made for it through this site. I also have a cover and I made a PVC frame for it. It stays in the slip in the front, in the water, all the time. I bottom paint it once a year.So, here is the deal. After a bunch of inflatables over the years, I decided they were too much of a pain and the PVC ones all disintegrated despite care. So, in 1985, I bought an 11' version of the Watertender and loved it. I also had a 2.5 HP Nisson. I sold these with my last boat and replaced the two with the same thing, just updated. The Watertender is reasonably stable. The engine is plenty for it. So, as to towing, I use a bridle from both stern cleats to the towing eye, attached independently for redundancy. Now, I am using a PWC tow rig I got at Boat US. In any case, use poly so it will stretch and float. I have been in big seas and following ones too. Only once have I ever had to lengthen the line to keep from having it crawl up my transom, and that was 10' seas and 20 knots wind at my back. I just used one of the bridle lines to attach to the other.The bridle can be adjusted to move the tow from one side to the other. In general, I tow it pretty close so it rides on the stern wake. I sometimes leave the OB on it if seas are decent. It tows fine and has little drag. Good luck. Rick D.