The failures of these previous models have led me to start making a new cardboard model. However, I have looked at the work of others and learned a lot since my last model. I have a new adhesive, some more accurate tools, and a whole load of pictures, as well as a new construction method. So here's my progress so far:
The tools I use (there is also a 30cm ruler, which I couldn't find at the time of taking the picture!
Also, one of the best parts of card modelling is the eating! I spent some time eating ice lollies, cereal, pizza, anything which comes in a box!)

First I sketched out the basic survival cell on paper, to scale. I must mention I am using a 1:10 scale for this car, as it allows me to include more detail. I also think it's a good size when considering the thickness of the card, and its 'bendability'.

I then sketched the headrest, and side cockpit dimensions

Then I expanded the sketches to include the whole survival cell, and a fair bit of guesswork had to be done in terms of dimensions and where the bodywork actually ends, since even the bodywork at the rear of the survival cell is made up of small pieces, which wouldn't be feasible in a card model without a robust fastening system (which I do not currently have)
so I decided to include some of the small panels on the survival cell, while leaving the big ones separate and removable

top view

First attempt at cutting and bending the survival cell didn't go to plan at all. The height difference between the cockpit sides and the top of the chassis meant that after folding, the cockpit sides would no longer be flat, but angled. So this piece went into the recycling bin

therefore I cut out the parts separately and bent them at the edges slightly, to ensure a smooth curvature after gluing

The survival cell taking shape

Further development of the survival cell

I will need to remove and remake the camera that looks at the driver, as this one became weak during cutting. it's less than 4mm long, and less than 2mm high.
that's pretty much it so far. a few things to mention: the survival cell has had some reinforcements added inside which are not visible in the picture, and this has done a lot to strengthen the piece. it's very rigid now. another thing to note is that I no longer need to make tabs at the end of card pieces to glue, the glue is very capable and can bond very thin surfaces. the entire survival cell you see has no tabs whatsoever. another very interesting thing for me is that now I have to plan what i'm going to do next, since a whole lot of construction depends on other things, such as paint, and carbon fibre covering, etc. For example, I cannot paint until I've cut out the holes for the suspension, and I can't cover the interior with carbon until I've painted. this adds another aspect to model making which I haven't encountered before, since the previous models I made were not of this complexity.
the model looks quite scruffy now, but it will be cleaned up with sandpaper and tape before painting
That's it for now, thanks for reading