I have used a similar system as described by Ray S for over 10 years..........
I used Whale components and 25 ltr translucent plastic jerry can for the tank.
This is mounted in the front wet locker and is secured to prevent movement.
Minimal weight was added to the noseweight, as the tank can be empty or near empty when towing.
The spare wheel has been move from the locker to a rear of axle carrier.
The locker is heated by a 12v 2" fan that transfers warm air from the living area of the caravan to the front locker.
This prevents the water from freezing in sub zero temperatures.
My system consists of :-
2 x 25 ltr translucent plastic jerry cans that can be used as above or externally in the normal way.
2 plug in pumps that can be used in either location, or even both together, as they are water pressure operated.
A fold up truck to transport the jerry can to the supply tap.
A made up short water hose and plug, so that the internal tank can be filled in situ from the other jerry can via the other pump.
In this instance the transferring pump is powered by a dedicated 12v supply in the front locker using a DIY electrical socket.
Personally I prefer translucent plastic jerry cans to Aquaroll's so this system has that added bonus for me!
I hope this gives you a few ideas.