camper trailer chassis frames

Haven't heard of Supagal but have used Duragal(which may well be the same thing)... Basically if you use the Duragal you still need to treat the welds, usually with a cold-gal spray can. Disadvantage is the inside of the weld remains untreated and you may still get corrosion from the inside out. Hot dipping galvanises both the exterior and interior of any tubing used in construction, all done after all welding has been completed.
Blue

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Supagal is galvanised inside and out by BHP at the steel mill. In other words the galvanizing is integral to the product and not relying on a coating. The other thing is that Supagal is HIGH TENSILE as different from most camper trailers makers who I understand use a mild steel chassis. High tensile is MUCH stronger and will flex where mild steel may break.

Some makers use a laminated (i.e. double layer) chassis because it is stronger than the same size in a single beam, e.g. a laminated beam in timber is always much stronger in a roof or floor support situation than a single beam.

You should not use a laminated chassis in blue steel and then have it hot dipped galvanised as the liquid gal will not flow between the two chassis laminations. They will eventually rust out as water enters the area between the laminations.

Some supagal chassis are also progressively laminated, i.e. it is thicker in the middle where the suspension is and thinner at the front and rear where the weight is less. This way the chassis is as light as it can possibly be but also very, very strong and totally rust free.

Yes it is quicker to make a single beam chassis and then ship it off to the galvanisers but the down side of this is that the galvanising adds weight, sometimes over 50kg. You may notice that these trailers are sometimes smaller in body size than a supagal build but weigh the same.

On most supagal built trailers the body can be welded to the chassis which creates a very rigid structure. Usually with a galvanised chassis the body is usually bolted on thus creating a weak point. Also used on some supagal trailers is an upper chassis, similar to monocoque construction in motorcars. The internal baffles inside the trailer supply rigidity to the sides and body structure eliminating flex in the box section. This ensures the seals do not shift on one another. Once the seals start moving, dust can get in.

Most campers today are built in the same way as they were designed 25 years ago. Comparing a supagal built camper to hot dipped campers is like comparing a 25 year old car to modern design. While this may sound like a bold claim a debate re gal and supagal chassis may not be worth bothering with as you or something on your vehcile will prob die first before the chassis on your camper goes!

John

Supagal and/or Duragal are a much lighter coating of Zinc applied to the base metal prior to forming and as such offer significantly less protection than hot dip galvanised, apart from the issue of untreated welds. It is available in both 250 and 350 MPa steel product.

It basically comes down to choice. Lighter gauge higher strength steel possibly means a lighter trailer however the down side is more flexing and more chance of stress fracture due to metal fatigue. Grade 350 is ideally suited to some areas of construction, but I have my doubts with regard to trailers etc.

Cheers

Don't know the technical differences between the products but have got a camper.

My trailer is 9 years old has been all over the place including plenty of creek crossings and lots of sand. Roughly 35000km in off road and rough dirt conditions.

I was told at the time of purchase that it was gal steel with the welds cold galled to restore the protection.

It is in pretty good nick considering what it has been through. HTe manufacturer said he used this system because if you build teh trailer and then dip it it will distort and then the seal don't seal.

Duncs