Gas Bottle sizes to suit a 680 and 600

[Black.Sheep.Cali]

Hi guys

We should be getting a GC600 for an upcoming trip as our GC680 has not arrived yet.

We have ordered a GC680 with diesel/electric heating but the loan GC600 could just have Gas heating.

I need a Gas bottle to suit but ideally would like to buy one that we could use in our GC680 after this trip.

What would you recommend?

TIA