We lived in our caravan in a caravan park for about 2 1/2 years however ours had a fixed island bed. You can use mains water plugged directly into the caravan however remember what goes in needs to go out and you will need somewhere to drain the waste water. Winter will be your biggest issue and you will use a lot more electric to heat the caravan. Unless you get a 45kg bottle using gas to heat the caravan will work out to be very expensive. I assume you will be paying the parents for the extra electric and water consumption as that is when things could go sour? BTW as there will be more than the parents living at the property council tax may increase. Use Dometic tabs for the toilet as you may need the toilet during the night. IMHO to get a reasonably decent caravan will cost you in excess of £2000, but remember when you sell it, you will probably get most of it back. I would recommend that you get insurance for the caravan even though it is going to be static. It should not cost very much for a £3000 caravan.
Our satellite dome weighs about 12.5kg and cost us about £1200 two years ago. To get channels south of Bordeaux you will need a large dish, but is the extra cost worth it if you hardly ever watch channels like BBC, ITV etc? We take our Sky box with us so we can record and watch programs. If deciding on a satellite dish or dome, make sure that it has a twin LNB.
We used a Maxview 55cm dish and found it to be adequate however due to the British weather being so changeable just before you arrive on site resulting in you getting soaked, we decided to have a satellite dome fitted. We know that is works as far down as Valencia in Spain although you cannot get the UK channels like BBC, ITV and a few others, we can get all the other Sky channels.
We have a 2005 Jeep Grand Cherokee 3.0L CRD towing a caravan with a MTPLM of 2000kg and towing at 50mph we can get just over 23mpg. The Jeep has two adults, mobility scooter and normal caravan stuff in it so think that is pretty good. I am surprised the Alhambra doesn't get more mpg when towing. We did consider replacing the Jeep, but the asked myself "why" so we still have it. LOL!
Wouldn't the cost of posting a few bottles of wine be greater than the cost of the cheques? Never used them so unsure what you could do with them. We are off to France in June but using ACSI campsites. Can a camping cheque work with ACSI?
Example: Exeter racecourse for two nights at end of the month £39.00. Commercial site nearby pitch with EHU, water and waste connections is £44. Worth paying the extra as the commercial site is a lot nicer plus water and waste hook up.
Don't forget that most breakdown covers offered with insurance policies do not include onward travel. Also if the caravan is in storage will they take it to the storage place, the car to the repair centre and then you home?
We have found the same thing with CC & pricing as many commercial sites some even better with more facilities than the CC are charging less. I guess they have to find some way to pay for the rebranding that no one wanted. However we remain members of the CC for Mayday, CLs and France ferry crossings as the savings outweigh the membership costs.
Most of the cheaper damp meters although very useful can be intrusive and tend to leave holes. The better one is the Protimeter which is what dealers use however that is very expensive, but it does not leave any holes etc. Your choice.