"Forty days of camping are hard."
Translation:Quaranta giorni di tenda sono pesanti.
Even though Italian may stress the plural of "giorni" and say "sono" here, the English "are" should be "is". It's about a period and not about 40 individual hard days.
It depends on your dialect of English. I would naturally say "Forty days of camping are hard", not "is hard".
Actually no :-) - grammar is very rarely a question of dialect. You may say "40 days of camping are hard", but that doesn't make it grammatically right, in my opinion. If you say "camping is hard" and then add "40 days of camping is harder", you can see my point. The talk is not about 40 individual days, but about a long period. If you say "40 days of camping are hard days" it's another matter, of course.
So would you also say 'The family is having dinner' is correct, whereas 'The family are having tea' is wrong? Both are correct, but depending on what you are used to one or the other might sound unnatural (perhaps because we are in different places of the world, where they speak different dialects).
ChristelDK is right, the 40 days together are a singular unit composed of 40 days, so an unit is not are. If for example you say "Seven days are a week" then it is ok to use are because you're saying that the seven days, each one as an individual unit, become a week.
Quaranta giorni di campeggio sono difficil - Fits also and its easier to remember that campeggio is camping rather than tenda. But I wonder why there is pesanti instead of difficili ? Does it has EXACTLY same meaning?