Jon, I also noticed that with passengers at the back they tend to ride a little bow up. I didn't want to fit fins because I wanted divers to get back in over the stern and they might get in the way so fitted a pair of these:
http://rib.net/forum/showthread.php?...highlight=trim
The effect was to lift the stern and lower the bow a fraction giving a longer planning platform and therefore more stable particularly when in strong cross winds which can also induce a lean.
They also reduce the amount of water coming up and touching the tubes at the stern.
Pete