I see the lunch box hinge as an issue but from the pictures they seem to have a pillow style O ring between the two surfaces. If it locks down tight enough then I see no leaks.

The way I am doing my 2 piece cover is .046" - 1.2 MM groove on both mating surfaces for RTV. Quick easy and no need to source a prefab gasket ring.

I will post photo's in a couple days.

EDIT: It was less expensive to get a full length flat bar of alloy rather than 6 pieces to make some rocker covers. Now I have enough for 4 rocker covers. 2 are spoken for and 2 are not.