Work on the steel frame- what it all sits on.

Once I had separated the body from the frame, I was able to get a good look at it.
There was some surface rust and where the stabilisers (the thing that you crank up under the back of the caravan when parked) attach, some of the metal had corroded.
The plywood frame had some rot at one of the corners, and the wheels had rubbed on the wooden wheel covers so needed to be enlarged. Therefore, rather than patch the plywood I decided I would replace it.
The plywood was riveted securely to the metal frame, so I had to crack the rivets off with an old chisel.
Once the floor was off I then removed the wheels and axels, put it all on a trailer and took it to be sandblasted, weld new stabiliser mounts, and drill out some of the holes (so I could attatch the plywood with  stainless screws from underneath). The frame was then sent for galvanising.

The alternative would have been to use a wire brush on a drill to clean the frame as best I could and paint it with something like POR-15 (POR-15 Link)
I knew this would not treat the inside of the steel box construction, I would not get all the rust out, and it would require more time. (This, however would be a much cheaper option by far and would suit those on a tight budget).

I will give a breakdown of costs in a later post soon.

The torsion arm  from underneath

Torsion Suspension 

"Torsion suspension is basically a swing arm style axle which pivots within a rubber or elastomer enclosure.
As load is applied to the axle the torsion arm turns within the rubber causing the rubber to compress on one side and roll on the other and as the load is released the rubber moves the torsion arm back to its original position.
This type of suspension can give a very smooth ride as the trailer rides over the bumps with independent suspension. Another advantage is that the trailer deck height can be significantly lower to due the lower profile of the torsion unit.
There are a few disadvantages to torsion suspension as follows. Torsion suspension load capacity normally maxes out at 2500kg towing capacity" From "Trailer Sauce"
We should be OK with the weight limit depending on what my wife wants to pack!

Now we have a solid frame to build on...