If it gets stuck open you just drive fast and the rain won't come in.
There are two pins you pull and release the top panel to slide forward.
The top runs with cables like a bike brake cable.
A gear drives the top from the housings on the cable, the wear is usually in the aluminum guide tracks.
Mine look really good though.
I'm trying the panel bonding glue in place of all the spot welds around the opening.
The box is supported by brackets screwed to the roof frame work so most of the weight is supported there.
Dave