I've got an old 20 litre, it's a cracker. Produces port you would have to pay bucketloads of cash for, with patience. The giant size lets you get good age into it. The longer the better!
A couple of tips...
- Towards the end of swelling your wood

(woo-woo)

, if you can deal with the shocking waste of alcohol, add a bottle of brandy to the water once the drips have stopped. It gives the wood a real headstart and will reward you for a long time to come. Then chuck more brandy into the port! (I use nearly a bottle per 20L)
- Give the raw product time. I find a great time to fill it is near the start of summer, when port's off the agenda for a while. By the time the weather gets cold again you've had a good few months of improvement happening.
- Some people top up regularly. I find this counter productive. Hammer it in the cold months, fill it when it gets warmer and leave it, then you'll always be drinking it with a bit of age.
- I let it get too low once. Oops. Nearly lost the barrel altogether. If it gets to a third full only, fill it.
- Langmeil winery in the Barossa produces some of the best bulk port in the state. It's already got a few years behind it by the time you buy, and with a bit of wood and time quickly develops into liquid gold.