The first thing you must do is to have a look in the owner's handbook of your car what the maximum permissible towload for your car is. (It's probably 1300kg). That is the absolute legal maximum axle load (not total weight) that the caravan may have. The second thing is to check the approximate kerbweight (for your Astra this will be somewhere around 1250kg - it doesn't have to be that accurate). For a novice, there is a general recommendation that the total weight of the caravan should not exceed 85% of the kerbweight, so 85% of 1250 or 1062kg would be a rough guideline figure. This would mean that you shouldn't be looking at caravans with an MTPLM (maximum technically permissible mass) of more than about 1050 to 1100kg and you mustn't tow one that weighs more than 1250kg plus the noseweight on the towball (usually 75kg for a car like the Astra), i.e. an MTPLM of 1325kg.
Some cars have a lower legal limit than the 85% weight ratio guideline figure so you need to know both.
Once you've done this little bit of maths you can go hunting around for a caravan within those limits that takes your liking. If all the above figures are correct (once again, check them in the book) then we are talking about 1050 to 1100kg as a sensible maximum for you and your Astra.
