I bought the 'shower cap' type for my 4/4.
The idea was to avoid using the roof or tonneau and just put the cap on.
Sadly, it pools with water and, as soon as you try to take it off you just have to prevent all the water from pouring into the cockpit, as I found out this morning. Oooops!
It looks very flimsy and as though it'll take off, but it seems okay generally.
Might try the one that covers the bonnet too!