Rusty gas tank

I have just noticed that there is a fair bit of rust along the entire length ( road side ) on the on board gas tank, I have spoken to the chap who has just carried out the habitation check but he was unable to give any advice with regards to it being safe or not, his only suggestion was for me to ring Autosleepers, but before doing that I thought I would ask the question on here first. I'm hoping that the tanks are double skinned but if that is not the case then to get to this state in 4 years is a bit of a worry. Any thoughts/advice greatly appreciated.

Batch

Does it currently have gas in it?

meanchris wrote:Does it currently have gas in it?

Yeh ------ well it did have last time I checked. 

I had a rusty gas tank on a five year old Renault Timberland conversion.  What was even more worrying was that one of the two retaining straps had parted through rusting. The other strap was well on the way. The tank was removed, stripped and repainted having first established that the corrosion was not seriously penetrative. I came to the conclusion that the original paint protection was of an "interior" quality.
I find it incomprehensible that a manufacturer could market tanks without ensuring that the exterior finish would withstand the very harsh conditions under a van. It is equally incomprehensible that a converter would fit one.
Keith

I posted about this common problem once but I cannot find the topic now.
The gas tank only has a thin coat of red paint.  Our tank was wire brushed, repainted and then sprayed with clear Waxoyl.
PeteJ

I forgot to mention that the rust is superficial because the tank is not painted properly but, as [You must be registered and logged in to see this link.] mentions, the straps can rust through which is bad news.  If you remove the tank, be sure to fit it at the correct angle or the gauge and 80% fill stop valve will not work correctly...
PeteJ

Just an up date,  I rang Gas-it yesterday and spoke to a very helpful chap called Nick, he confirmed that the gas tanks are single skinned, made from 3mm steel and powder coated and that it is not unusual for paint to be bubbling and showing signs of  rust after 4 years he also stated that it should not be a safety issue. His advice was to remove as much paint and rust as possible  with something like a plastic  ( not metal ) filler knife and if using a wire brush not to be to heavy handed with it and then spray as much of the tank as possible apart fom the aluminium cover with body shutze. I couldn't get 3m body shutze locally so I got a spray can of Hammerite under-body seal I would imagine that it is something similar and as an added precaution I'll coat the rust with Kurrust or something similar  prior to spraying the underseal. If I get a chance I will post some before & after pics. 
Thanks to Keith,Pete & Mean Chris for your replies. 
Batch

Hi Batch, used to do a lot of car repairs/ welding and found that treating with kurust by all means  then give area 2 coats of davids isopon zinc 182 zinc rich  rust primer held back the rust for a good while. I would then paint with something like hammerite then coat with the waxoyl. Body schutz was always avoided like the plague in the trade as yes it gave a quick coat and covered a multitude of sins but if damaged , water creeps under the coating causing further unseen rust damage. I agree with you in that if the maker says that powder coating wont last over  4 years on something as important as a gas tank then perhaps they should be looking at another method of rustproofing . My Kemerton ( 2014) interestingly is powder coated red but the bottom half is coated in what looks like body schutz. It is now sprayed with waxoyl as well to try and keep the damp out.