Each DIY Packraft size is a different design, and because the side tubes are not parallel (the front of the boat is narrower than the back), you cannot lengthen or shorten the cockpit without completely changing the geometry of the boat.
To visualize why (in a simplified example), imagine an isosceles triangle with a horizontal base and a height of 10 cm, and then imagine you want to reduce the height by 2 cm. If you shorten the sides then you also have to change the angle between them and the triangle‘s base to keep it a triangle – if you just shorten the sides but keep the same angles then there will be a gap left at the top where the two sides should meet.
Because the packraft tubes are curved in 3D space, changing the length is not a matter of straight lines or even simple curves – it’s a complex 3D problem, best solved by a computer.
The Voyageur 2-person DIY Packraft is the exception – it has parallel side tubes and, therefore, the length can be modified without much difficulty.