Sorry about the error of using stress when it should have been force (It was late, no . . .I was tired, no . . . I forgot, no . . )
Check out
http://www.inboardtalk.com/tower/tower.html and see the stress analysis link at the bottom. In summary with a load cell being used to measure the exact force, and advanced skier was pulled through a slalom course and the force on the rope never got over 600 lbs, certainly pulls a boat around much more than a wakeboarder and would not expect a wakeboarder force to be this high.
This resulted in a 300 lb downward and 50 lb rear force at the rear legs (with a 2" x 3" base plate the sress on the deck is 50 psi). The front legs are less of a concern since the force is UP but it is the place where reinforcing the underside of the boat is most important.
If your building a tower for a fishing boat they have mounts both on the floor and side of the boat/console so the issue of side stresses are well covered. It would be the same as mounting the tower to the floor of the boat and then having additional mounts on the inside at the top of the gunwale.
I agree with the use of Heim Joint which is why we chose to use them on the Monster Tower. This is even more important on a universal tower often going on boats that were made with chopped glass and not hand laid like higher end boats.
Heim joints make sure the force can not torque or twist the mount, and most of the tower builders have gone to them, especially for universal towers.
Thats my opinion but I could be wrong.
Bill
www.MonsterTower.com