Caravanning v cottages

Hi everyone, I have been doing a bit of research on caravanning but would like some advice on whether it is cost effective.

At the minute we holiday in holiday cottages. We holiday in the UK and normally have two to three a year. This on average costs us around £400-500 week. We have two estate cars (Volvo 940 and BMW 325i). From my research they will both tow a similar weight. Neither has a tow bar so this will need to be fitted. 

I work a shift pattern of 6 on 4 off at the minute so could go away either mid-week or weekend but am limited to school holidays and weekends due to having one child at school (aged 5). We also have another child aged 3. 

I believe I will need to have it serviced annually (£200?), storage (about £400?) and insurance (£150?) How much would a week at a caravan site cost?

We would be looking at spending around £4000 on caravan. I would go for something cheaper but damp is a worry. We would like 4/5 berths.

Sorry if it's a bit disjointed as I'm typing as I think about things! To sum up, would it be cost effective to take up the caravanning lifestyle??!!