It depends where you're setting off from, and whether you're towing or not. If you live near Newhaven then it may make sense, if you don't mind spending more money.
The Dover Calais (or Dover/Dunkerque) prices can be quite cheap - our crossing was £58.00 return, for car and caravan, including two people and the crossing takes about 2 hours. Looking at the LD Lines website, Newhaven/Dieppe with a caravan may be upwards of £300.00, and take four hours. Two hours journey time from Calais (the additional two hours 'before' the Dieppe ferry would arrive) will take you south of Rouen - so you'd be further on your way using the shorter crossing, if you set off at the same time! From the LD Lines website it would appear that you have only two crossings per day - 11.00 (ish) and 23.00 (ish). The day sailing would get you into France at 16.00 hours (ish) - and you'd still be three quarters of an hour away from Rouen! The Dover/Calais or Dover/Dunkerque sailings are approximately hourly - so you have a much wider choice of sailing times between the three operators on that route. Another consideration would be to use Eurotunnel - if you shop at Tesco then their Club Card vouchers can be exchanged for deals which can be used towards the cost of a Eurotunnel crossing.
Years ago we used to use the Newhaven/Dieppe route, when prices were roughly comparative with the Dover/Calais crossings, but these days we just go for the cheaper option. Driving in France is infinitely better than driving in Britain anyway.
From our experience this year, we found setting off from the North of France in the early morning gets you about half way to the Dordogne in time for a pleasant overnight stop. This year we stopped at Vatan, just off the A20 - a nice municipal site, absolutely a doddle from the motorway, and had an easy run to a site near Belves the following day. If you're setting off later in the day then you'd be looking at a site a bit further north, but recommendations really would depend on your arrival time in France and how long you could drive the first day.