I have a 500ltr upright tank,he did say that yours was quiet tricky to do.Surely he will know what is best for my setup,he certainly sounded like he new what he was on about on the phone.Are you talking about pre heating the water on the way to the first job wayne or in general use.
Mine was quite tricky to get at because my tank is covered in insulation with a 18mm ply board on top where I've mounted a second hosereel, battery box, battery chargers, battery inverter and a few other bits and bobs.
Yes he does know what he's doing, rest assured.
I was on about pre heating the tank. I only pre heat my tank when I'm doing delicate glass when I don't want to use hot water direct from the heater and when it's freezing so that my pump will start in the mornings and to stop my hosepipe from freezing.