From what I've both heard and read, putting a velo body on an existing trike is a sub-optimal solution for the most part. The reason is that most trikes are not suspended, at least the most popular trikes to add bodies to are not. Having suspension on the rear is an important safety feature, because it's easy to lose traction in the rear, say from hitting a rumble strip or a buzz strip. When that happens, without sufficient damping, the velo will quickly lose control, either flipping or swerving uncontrollably. There was a video out there somewhere of somebody losing control that way, fishtailing a few times, going on his side, and actually grazing an oncoming car's tires before coming to a rest in the middle of the road. Scary stuff!