Look for bubbled paint, a sign of "cancer". To remove it well you need to either cut it out or go nuts with a die grinder to clean all the old rust out. once its clean and should look like shiny metal spray Etch primer, maybe a few coats them primer then paint what colour you want.
If you're concerned about rust that may have been bogged over, grab a magnet. Bog is porous so any moisture getting onto that will rust out the underlying unprotected steel. So if the magnet grips there's no bog there. If it doesn't a repair has been done there with bog and that's a likely candidate for rust. For the VB-VL check the rear quarter panels down low, door skins down low, the spare wheel well, the boot floor and around the rear window. Also, look for any paint bubbles, that's the starter because there is a volume expansion when the iron in the steel oxidises (rusts).
Any moisture in the atmosphere will attack exposed steel so covering it up won't help much. Where have you got water leaking? As to temporary fixes, for any interior stuff where you're not worried about the paint finish scrape off/grind all the rust scale you can and try rust converter and/or fishoil. That will provide a reasonable barrier. A more permanent measure is POR-15. But the only true way is to cut out the rusty piece and weld in a replacement section.
i think demons has summed it up pretty good. on my vh, it was rusted in the following places -
rear corners of the front doors
passenger side sill
spare wheel well
the panel under the bumper
the bumper mounting brackets
passengers foot well
passengers side rear wheel arch at the bottom front
the panel at the base of the windscreen
windscreen frame - both front and rear
around the tail lights
there was a hole or two in the panel where the number plate goes
rear passenger side floor (that had been cut out and replaced at some stage)
the roof had surface rust
that's about it. i have a feeling it was used to launch boats.
thanks guys ^_^ only rust so far i have found on the vh is near the back wheels under the door.. praying theres no more! lol. they have tried to cover it by painting an inch thick coat of black paint over the top. *shakes head* but owell not bad for 300 bucks
Look at my x project site area mate, ive done rust work in part 2 the infomation there might help..
Finding rust is upto you take a closer look eg. bubbles in the paint.. if u find spots just tap lightly with your finger around the area and see how far the rust area is on top, you won't know how deep it is until your grind away or sand.. You may even be suprised that most of it could just be surface rust, the top layer..
The boot is a different stroy and there's a few ways u an go about it which is upto you.
a biggy to keep an eye out for is rust under the bonnet in the well near ur interior fan. on each side there is a drain hole, but this can block. then the water makes its own hole and low and behold, u have water down the main door pillar.