In case anyone's interested...
Although I'm not (yet) a motor home owner (I joined because there have been useful postings about Irish Ferries and the WB Yeats), I also read with interest the postings above about tolls.
If you're not aware, you may be interested in a tolltag (as with our motorways in the Republic) which is available online and covers motorways in France, Spain and Portugal - you can also add Italy, if you wish.
I have been using one in France for years and added Spain and Portugal without a problem last year. Stated simply, you provide the necessary details of self, vehicle and card for payment; they send you a tag to mount on your windscreen and you breeze through the toll stations in all 3 countries. Car drivers can use the express lanes common at most toll stations, though I'm not sure if a motor home can. In any case you avoid the card/cash business, right hand drive problems etc. - the barrier just raises as you approach. The set up cost is a reasonable €15 (€11 for activation at first use and €4 for postal delivery of the tag to your home address). The actual toll charges are made on the card you provided in the month following use, plus a charge of €2 to €3 for each month used (no standing charges when not used).
My French is sound enough but a disadvantage for some will be that the site is in French and I couldn't find an English version. However, Google translate might help or,even better, a friend or acquaintance with a reasonable grasp of the language. The site is:
www.aprr.fr/fr , though I believe there are other firms who offer the service...