Hi Andrew we are also a family of 4 with a Zafira and we managed for a couple of years without a roofbox , managing to fit everything in. As others have said you just need to be smart with your packing, using every available space. We put our cool box at our daughters feet then cover it with a blanket so she has her legs out straight. This may be the last year we get away with that tho as she's getting really tall!
Good luck, sure you'll be fine for a few trips anyway! Until the old camping bug and "need" for equipment bites you!
Unfortunatly I cant really give any practical advise as when solo camping I manage to fill my small estate just for me and dog just a thought.. could you maybe box up the kids and send them down by courier..give loads more room in car..
The Handirack and handiholdall system is really good if you do decide you need a bit more room. All, our beds, bedding and clothes go easily in ours. That way we don't feel to squashed in the car which can lead to arguments!
I couldn't possibly get four people and kit to camp in reasonable comfort for seven days in my CR-V and I don't take nonsense like fridges, toasters, microwave ovens etc.
Would it be possible to take one passenger and send the other two by train which is what I do?
Tesco/Sainsbury delivery. Donate left over wash up liquid etc at the end.
Ikea small cushion about 80p use as pillows and vac pack.
Vac bag for most clothes.
Leave out the footprint and use cheap dust sheets.
Forget the fancy kitchen units and cupboards - useful but take up space and weight. Simple folding table and cheap zip up shopping bags from pound shop for storage.
Sea to Summit stuff is expensive but fab.