I think that the GVW is the maximum weight that the trailer (including itself) is designed for, while actual weight as measured on a weighbridge (easy to do) is the real life amount to take into account as to whether you’re in the clear or not. So if your trailer GVW is 1,800kg, unless you have even more extras on board than Rob, you should be OK as far as the trailer is concerned.
A while back, several GRP BR20 and BRe owners (including me) found out on weighbridges that their boats and associated gear were very close to the 750kg GVW limit for their unbraked trailers. They opted to have their trailers upgraded to braked, which helps the tow car (eg when going down steep hills) and also puts less stress on parts of the trailer like the bearings. The downside is that the brakes need servicing at regular intervals.
Assuming that your real life trailer weight is 1,600 kg, if you get a car with an all-in weight of more than 1,900 kg, then you’ll be over the 3,500kg limit. It sounds like the XC90 with occupants would be well over.