Travelling will bring about many oppurtunities for learning naturally, I know my daughter learnt about distance and orientation from our 'talking map' for example if you're using a gps at all which can then be a jumping point for looking into it at depth. But it is a commitment to constantly be noticing and acting upon the opurtunities and having the patience to involve children in lots of different things (such as helping plan with maps for example or with money transactions) and it won't be linear or consistant in a similar way to school which might be hard since your kids will need to transition back at some point.

My advice would be to get a Maths and English program if you are concerned about keeping up in order to make the move back into schooling smoother and then just build on topics of science and history and geography and health/physical ed as they come up or as you feel it might interest the kids. Do you need to do a language? Can't remember if that's a year 2 or 3 thing. You can access the national curriculum through the government site to check what you'll need to cover. Depends where you're travelling to too. Also depends what state you're registering in as to what sort of plans and proof you'll need to provide.

I don't know anyone that used premade curriculum though unfortunately. Someone might see this though after my response bumps the thread hopefully that knows more about that.