When I did my conversion I had to order 1 reinforcement plate. They are, of course, available through a Dodge dealer. Mine cost me about $17 about 4 weeks ago. And yes, due to the size of these mirrors, the nuts for the standard, non-towing mirrors won't work on the new ones - they are too small.
Because the wiring when fished through the 2nd gen base bracket exits at a little different point than the standard, non-towing 2nd gen powered mirrors, I had to drill a hole through the metal behind the base to fish the wires through into the door cavity on my '98. No big deal and its all hidden when done.
-Jay