Don't know where I read about returning the box, thought it was on mhf!if you are over 3.5t you need a go box. When i got mine they asked where I was going and told me how much this would cost. They told me to watch for the beeps and what they meant. They gave me instructions that also re-enforced the message. I'm real thick but understood it.
Also you do not have to return your go box as stated above. You pay for it and you keep it, mines still on the windscreen, it looks cool.
On fines abroad. I had 3 sent to me for speeding on my Vespa across the bridge in to Venice all over a 2 day period. Still waiting my court date some 2.5 years later. My mate that used the Brenner toll and jumped the gate is still waiting his court appearance from the same trip, he missed the turn.
However, what I would say is that if you get a ticket abroad, and you intend on going back there with the same number plate having not paid the fine, expect to be pulled, now this has happened to someone I know.