Tendonitis can occur at the wrist of your feathering hand. It causes swelling and pain and sometimes you can even hear a noise as you flex your wrist. It is more frequent when we paddle in windy conditions.
Bum pain occurs when the muscles of your buttocks are deprived of blood after being in a sitting position for a long time. It can be quite debilitating.
You need to find a system of prevention that suits you, so do plenty of long paddles in your training and work out a system that suits you.