what we normally do in my airlines for tankering especially with 4 to 5 sectors,we work backward(from the last leg) we take the minimum fuel the OFP tells us or we decide the minimum fuel we want to have in the tanks upon landing from the last sector,then we add it to the differents trip fuel on each leg except the last sector, we add taxi's and Apu.That gives us the whole tankering we need in order to do all sectors(provided of course) payload allow us to Tanker otherwise we refuel when needed at intermediate stations.
The way i was shown is to take the (MALW + trip Fuel) which gives me the Max Tow which should'nt be exceeded otherwise i'm Max landing weight limited and compare this one with the (zero fuel weight of the 1st sector + the total tankering fuel) and see if it exceeds the(MALW + Trip Fuel)
Another way is to take (Malw + Trip Fuel) and substract it to the current ZFW and you get the fuel required and always crosscheck it lies around the estimated value given by your OFP
However i'd like to know if there's any special tips how to calculate RTOW other than going to the performance section?