Hello Sue,
The gross train weight is published by the manufacture, it may be in the owners manual or sometimes it is included on a plate fixed to the vehicle, along with axle loads.
I will not try to second guess the figures, as you must check with manufacture.
As Lutz points out, the published kerb weight can be significantly different to the actual figure for your vehicle. The other twist to this is that the way a kerb weight is calculated. It bears little reality to the weight of a vehicle when it is being used, especially when loaded for a holiday. The important figures are the gross train mass, The max vehicle mass and the max trailer mass.
Non of these must be exceeded, and it is important to note that some manufactures GTM is less than the sum of GVM and the MTPLM of the trailer.
The 85% figure that you may hear about is only a sensible guide line, not a legal requirement.
You must seek the relevant figures from the vehicle manufacture.