I have seen many DIYs but this one deserves a big applause for the quality and attention to detail. Great job! Some suggestions from my side to reduce weight, get fibreglass cupboards instead of wood and acrylic instead of glass windows.
As for the rear I think the brake and indicator lights should be much bigger since the smaller lights might be difficult to see in poor weather conditions. Also put a reflector on the back, especially around the edges
How does the braking system work. Does it work like a regular caravan or did you design it differently?