We put a tower on our old boat, and it ended up being closer to the rear. We wanted it in the normal even-with-windshield position, but the shop but the front end where the back mount should have been. Anyway it ended up not being all that bad, though it did look a bit strange. It seemed to pull fine, but it did have a tendency to get the rope stuck in front of the racks when pulling around to get a rider. But if you're careful you should be fine. I would still recommend going for the more forward position, but if you really want in the rear (actually easier to get the boards down) you should be okay. Here's the pic; it was a 20 footer as well.