Coming from a static caravan, I would think very carefully about the size of folding camper you are after - my parents changed from a six-birth F/C to a 4-berth when there was 'just them and the dog' - it lasted less than one season before they gave in and went back to a 6-birth. My first f/c was a 4-birth (Conway Challenger, fore-runner to the Countryman), but my then-husband and I couldn't wait to get a 6-birth as soon as we had a car big enough to tow one, and there was only two of us at the time! The problem is the layout - the kitchen is effectively IN the seating area, so the non-chef (and the dogs!) is 'under the feet' of the chef,and once the table is in place, you can't turn round! Plus there is very little room to 'stretch out' and chill if the weather is not good enough to sit outside and you do not have the awning on. The 6-birth f/c have the seating/dining area separate to the 'kitchen' area. Have a look at the Pennine Leisure website - there are layout diagrams and interior photos for all the current Pennine and Conway folding campers on there. I realise this is only my opinion, but it's worth thinking about - there is more difference between a 4-birth and 6-birth f/c than the number of beds!
Have you considered a folding caravan ? We are selling ours it is on ebay at the moment so if you are interested take a look do a search for 'folding caravan' and you will find it. We towed it to start with with our 1.4 Renault Megane. We liked it very much and it rarely takes much longer than a normal caravan to set up once you get the hang of it. We have decided to go for a tourer and site it permanently on a site we have found that we love in Ripon.
We are not far away from you - caravan is in Wakefield in storage at the moment.
I'd certainly recommend a Dandy but I'd also go for a 6 berth not a 4 as we used to find that 2 of us and a dog filled our 6 berth! Imagine how it felt with 2 adults, 2 kids and 2 dogs!!! Sadly now only 1 dog