As a serial convertible owner, I am surprised to see such little bracing on the underside; even my 1991 Golf had a pair of RSJs reinforcing the sills.
That feeble cross member under the central box may as well be made out of tissue paper as it will add little if any a torsional rigidity... you need very thick metal to prevent the body twisting between the front and rear diagonals.
The orange sections of the body work are added strengthening to the body shell of the Golf cabriolet, and even then, they had a roll-over hoop to add rigidity.
The below are the areas of reinforcement in the MK1 Golf (The darker grey are reinforced, or extra panels installed by Karman