Rolling means that the next 180 day period doesn't start when you used up your 90 days. It's any 180 consecutive days. In your example you would have spent 78 from the 1st of April, that means that you only have 12 days left until 180 days from 1st April. i.e. if you go for more than 12 days before the end of September (give or take a couple of days) you would be over the 90 days. After end of Sep. (i.e. 180 days from 1st April) then you start a fresh 90/180. If you do get stopped, tell them the truth, that you really thought you had another x days. I'm sure you won't be the first to have got it wrong.It’s at home. In the uk. It’s left for a short time on its own. Jan 1st. Fly out have a long weekend. Fly back home. That will start the clock ticking April 1st drive MH into Europe for 78 days leave it at a park for three or four days your choice fly home and that will have completed your 90 in 180. Then return and complete your first 90 in the next 180 and drive MH back home.