Progress report:
The chassis we bought was delivered.
The next day I decided to cut away the old floorboard.
I cut off over 1 meter of the chassis with an angle grinder.
Since the trailer is due for maintenance I installed new lights to the chassis.
This will be fitted to the teardrop in the future but the chassis is now compliant and I can haul it to the shop for maintenance.
Unfortunately ply comes in different sizes, but not in the same thickness as insulation. I rented a polystyrene cutter and cut 4 100mm by 1000x2000mm thick sheets in sheets that are the correct thickness for walls and floor. If all goes to plan all the wood will be delivered next friday so I can continue my build. Unfortunately the cnc-company cancelled my order so I will cut the plywood to correct size myself. Should not be a problem, just takes more time.
Next week the chassis goes away for maintenance. The axle will be refurbished, new tyres will be fitted and shock-absorbers will be installed. The latter is a necessity to be allowed to drive at a speed of 100 km/h in Germany with the trailer attached.