I think generally speaking if you are 3500kg or under you won't need an On Board Unit. As we are over that at 5000kg I have previously used one in Poland and the Czech Republic. I avoid using one in Austria as the non toll roads are usable for us without having to go on paying ones.
In Spain, Portugal, France and Italy you'll just pay the fees at toll booths, Class 2 in Spain, France and Italy certainly as we have not been to Portugal in the MH. If you have a TAG axle you could get stung for a higher fee. I use a Bip&Go tag in these countries (one tag covers all) which makes life much easier. There are numerous tags on the market but if you fancy a Bip&Go one drop me a PM and I can get you a code giving you €4 off your first bill (I get it too).
We usually make 2-3 trips a year. There is no fee on most tags for fallow months so it only gets a use charge for the months you use it...maximum of 2 chargeable months from memory I think.
