[FL cruiser]

I was thinking why not just go ghetto style and put the oil jugs on the roof with a reinforced fuel line leading down the side of the truck. This way it's gravity fed, and I don't have to worry about tank filling (I just have to lift the damn thing up there!)...

I tried that. Vehicle was too top heavy and not fun to drive. Moved the tank inside to the rear cargo area. No smell. I still do load up the roof rack with extra containers for long trips though.

An unheated fuel filter will gel very quickly even in SA.

I have run unheated filters for a few years. They only gel quickly if there's fat in the WVO. With good clean veggie I can go three thousand miles before they gel.
With fatty WVO, it will gell in a couple hundred miles.

Won't the veggie oil corrode them?

It SHOULDN'T corrode if the WVO doesn't have allot of fat in it.
In the very beginning I did have the problem of the metal parts in my injection pump pitting and corroding. Fat particles would polymerize on the steel parts and pit.

Solved the problem with better settling and filtering technics. Getting all the fat out. Also got a different WVO source.