Hi Colin,
A T200 will carry a 625kg payload, including you, fuel, roof rack and all your equipment.
If you are of average weight and you 'travel light' then you should be able to run a van with a full 400 litre tank, but you probably won't have much to spare payload wise.
I wouldn't run a fuel tank of fuel and would start with your closest houses first. I would only fill it fully on the days when you expect you will use it all and just fill with it with what you usually use plus a bit on the other days.
My son in law has just bought a T220 LWB and is putting a 500 Litre tank in it. Its a 2004 75hp Tddi engine with 40k on the clock and an 825kg payload. It's in immaculate condition. We have just finished painting the back with Protectakote.
Spruce