Fishoil is very good and is a thicker substance that WD40. As the name suggests it does smell a little for a day or two. We have used it before on 4WD's. It's generally used for unseen areas
though as it is an oily coating. I wouldn't use either product on the engine bay unless it is a scrappy paint damaged bay in the first place. Both would attract dirt and dust and look foul
certainly not for the restored or show car.
Tectol have some very good products also but they are a little dearer. They have a spray for the inside like in the doors roof etc. Can't remember the name (they often use numbers)but last
time I bought it it was a yellowy liquid. It's also sometimes called body shutz and comes in its owwn gun ready for air compressor. The other is 556 I think and it is a tar based product that
you use mostly on the undercarraige and inside guards etc. It never quite sets and attracts a film of dust which seals it. Sounds bad but is perfectly designed for underbody. You can touch it
OK but if you rub it hard it will stain your finger. It's better that a hard seal as it doesn't chip which allows moisture under the skin. you can even paint over it if it is clean but I don't
know how long the paint lasts.
The fishoil will need reapplying periodically.