Good morning,
Long-term readers will know that I have recommended the use of de-odorised fish oil to rust proof the interior of vans etc. The brand that I have used in the past, K&H fish oil, is no longer on the market so I used "Septol"-brand fish oil for my latest van.
It's now 8 days after an application and the fish oil it is still tacky, meaning that any dust/dirt in the air will stick to it and look very unsightly. Also, if you wanted to paint over the fish-oil, you'll have to wait a long time until it sets before painting.
The K & H product was dry in 3-4 days. I'm very disappointed with the drying time of the Septol, but, if your own project can accommodate the extended drying time, then go for it.
I've still got one interior panel to cover and I'm going to use Valvoline Tectyl 506 which, like the Septol product, is available for SuperCheap stores. If anybody is interested, I'll report back on the drying time.
The reason fish oil is effective in protecting against oxidisation is because it does take a long time to dry out
I have a 20ltr drum of pure fish oil I got from a fish meal plant years ago and I use it for inside chasis rails and under floor areas. It works very well and remains "tacky" for years. If it eventually goes hard it needs to be re-applied. No good for painting over.
I reckon the K&H product would of had a low fish oil content.
Not saying it wasn't a good product.
I've painted over fish oil 24 hours later when it is still quite tacky. The paint sticks really well and dries out ok in a day or two, depending on temperature. It then works well for donkeys years probably because the fish oil underneath remains flexible or something.
I've done this inside car doors, under floor pans and places that are not for public consumption.
You would need to do a test sample first in case it doesn't work with the fish oil you're using, but I would expect iof brush cleanup for both products is done with turps then it would be ok.
Thanks for the opinions, guys.
Gwendy, my old van was 11 years old when I sold it. There was no rust in the load compartment where I'd fish-oiled the floor, roof and side walls, but the (not fish oiled) securing screws for the doors and trim panels had rusting of the screw heads, even though the screws had been cad plated. Also, the cad plated door brackets had started to corrode badly. Based on my experience, the K & H product was tops and I was really disappointed to find it was no longer available.
So, inspecting the Valvoline Tectyl 506 can, three things were noticeable: 1. the product is a medium brown colour. 2. It is supposed to last about 5 years, then be re-applied.
3. The drying time is 30 minutes. I've used it in an overhead compartment and it was touch-dry in about an hour. Only time will tell whether it is durable.
On a trip to my garden shed, lo and behold, I found an unused can of K & H fish oil! 
It was still pressurised, so I've sprayed it on all the exposed bolt, screw heads and door bracketry I can see in the load compartment, plus a few in the driving compartment. Touch-dry in about an hour.
Now for the board racks.
