Hello Tentmonster.
Whenever I read of a Renault as a tow vehicle, an alarm bell tolls. A number of Renault models have their towed weight limits (how much they are supposed to be able to tow) quoted in a rather unhelpful way. They can only pull their quoted maximum towed weight when the car is at its unladen weight. Which means for every kg of load (passengers, luggage and trailer nose weight etc and the weight of the tow hitch assembly) you put in the car, the permitted towed weight reduces by the same amount.
The only safe (legal) way of checking is to find the car's weight plate (usually located in a door frame or under the bonnet) and looking at the the largest figure (Gross Train Weight) and subtracting the second largest figure (Gross Vehicle Weight) and the balance is the maximum trailer weight the car can safely tow when loaded.
Regardless of any other advice you must not exceed the manufacturers technical figures above.
Now only when you established the cars technical capability can you start to consider what weight of caravan to look at. The industry advice is for a novice tower to look for a caravans whose maximum possible weight (MTPLM) is no greater than 85% of the tow vehicles unladen weight, but again in some Renault cars the maximum allowed towed weight is already less than 85% of the car's unladen weight.
So your starting point has to be with the cars detailed specification.
Even if you can work to 85% of the 1306kg (= 1110kg) as a maximum caravan weight, you are going to struggle to find a 5 berth at such a low weight.
In reality I think you will need to look for a more capable car.
I'm sorry to bring a note of caution, but there is also another matter relating to damp in caravans. Especially as you have stated you are looking for 15 yr old caravan you should definitely be ultra careful about damp issues. I will be surprised if you can find a 15yr old caravan without some damp issues.
I note you purchased a 'damp meter' and again I must post a note of caution. Cheap meters will not be properly calibrated and their results cannot be trusted implicitly. The wall coverings in caravans can give false readings to measurements, so having a damp meter is one thing, but knowing how to use it and to account for the materials you are probing is another.