They should be tight to stop the cover flapping, however, take great care when pulling on them as it is quite easy to overdo it, and tear the cover around the fixing point of the strap. Sooner or later you will do this and end up like the rest of us with the odd 'hole' here and there. You do get patching material when you buy the cover bt I have been lazy and just left it.
You will also find when you take it off, that the top will be covered in green slime. It is a good idea to try and jet wash as much of this off as you can, before storing it for the summer, however again try not to get the inside part too dirty. These things are big to handle and if the wind is blowing you can take off, literally.
However, it is worth it to keep the van in tip top condition.