Ok I know it will not be ideal but towing with a diesel Astra will be possible will it not? The van will have to be light and smallish any ideas on weights?
I used to tow an old Elddis Whirlwind with max weight of 800 kg with an Astra 1.6 petrol (old F reg) then with a R reg (97) 1.6 petrol. They both did struggle a little on hills, but did North Wales and many times to the Lake District.
Nobody can make any serious suggestions because you still have not posted full details of the car you actually have. If it is a modern diesel Astra you can go to about 1100kg which gives you a reasonable choice.
Just one word of warning... I have a 1.9CDTi 150 hatch that I was using to tow our van when we first bought it... It towed it well with no problems...
But since then the car has had to have new rear springs (One of the existing ones snapped) & then a completely new gearbox as it started making some scraping noises in 3rd & 4th gear... Luckily this was all under warranty!
On reading a few other forums - Astra Owners Network - for one, it appears that the gearbox & spring failures are common on this model of Astra, it has a high torque & some say that the gearbox is really only just strong enough to cope with it... so adding the weight of a caravan on the back, MAY - and only may, have attributed to the failures...
I still have the Astra as i love it... but we have changed the wifes car for a Nissan Xtrail so we use that to tow with now.