Heya Nick,
I'd stick with the fish oil fella, trust me. I've been using the stuff on the doors etc of my EJ for over 5 years now and even though the stuff once sprayed initially smells like buggery, I'm yet to see the slightest evidence of rust appearing (ie: it works).
Just remember to keep any drainholes cleared as I've noticed that fish oil CAN block the drainholes if the stuff is sprayed on a little thickly. I'd agree with Aaron, best not to go any higher weight-wise than mixing fish oil and sewing machine oil.
Cheers ...... Pete