From a "Live chat" with DFDS Ferries =
You are now talking to Steve - How can I help you?
You said: Hi Steve, we are planning going to France in our VW camper from mid September, we do not have a fixed date to return, likely stay will be 4 weeks. Question = can we just arrive at the Ferry for the return journey and "pay at the gate" or do we HAVE to book it in advance ?
Steve: Hi - we can only confirm a reservation with fixed dates so i would recommend booking a one way journey.
Me thinking "What the blithering heck does that mean ? it doesn't answer my question at all"
Steve: You can make a reservation at the port but the rates are higher, for our best fares visit
http://www.dfdsseaways.co.uk" onclick="window.open(this.href);return false; in advance
Me thinking, "I am already there !! or I would not be on your "chat" thing !!"
You said: one way out = yes I understand - how much higher rate for paying at the terminal - is it a lot more, up to 50% more would not be a problem
Steve: It can be yes
Me thinking "What the blithering heck does that mean, A lot more, more than 50% more, what ?"
You said: Sorry Steve, "it can be yes" = ?
Steve: it depends on space and availability but yes it can be up to 50% higher
Me thinking "so if there is no space then I might not get on for xxx crossings ? and "up to 50% higher" could be 5% or 50% so not very useful info there !"
You said: OK, so I think you mean it would be much better to try and book the return from say an Internet Cafe in France a couple of days before we want to come home, yes ?
Me thinking "I might as well not bothered asking"
Steve: Yes, this is my reccommendation
Me thinking "Oh, is that what you were trying to say !!! (and you are rubbish at spelling !!)"
You said: OK, Thank you, we will do that then, Bye
So, took a while to get there !! Jeez, it was a simple enough question !!

The answer to my first line should have been "YES" or "NO"
It looks like the best option is to find a computer a couple of days before we wish to return and book a one way ticket back. Or, try and do it on my "smart" (sic) phone - which I hate, and am not sure about using it in France re data charges ?
Shame they don't do an "open ended" return ticket, I would have thought that was quite a common request ?
Aside = I actually use an 8+ year old Nokia 5140 as a "phone" I like that, it has lots of advantages - I only use my fancy £400 HTC as a music server to the vans stereo when camping, it does go on the internet but is very fiddly for an old git like me
