If you mean strapping them to the tow vehicle there are quite a few companies that sell rack systems (gutter, non-gutter) that will then provide rails to attach the supports for carrying the canoes or kayaks. Yakima, for example. Most people put these on the truck's cab as far forward to avoid contact with the trailer when towing.
Can you describe the pads you are talking about? This might make it easier to refer what company provides the rack and rail systems.
DO NOT put these on top of the fifth wheel. The trailer is already at the height limit for most States. If you have a bumper tow you might make it, but with the wind forces and height requirements you might want to fasten these to the tow vehicle, plus it will be a lot easier to remove. Avoid the trailer's ladder.
Here is a website you can start with. You'll probably need a system that carries the canoe/kayaks as far forward as possible. There might also be a concern if your canoe/kayaks are very long to not interfere with the trailer behind you especially on sharp turns.
http://www.rackwarehouse.com/