Elliott,
The internal LL system indeed makes for a tight seal. One of the great features of a Leidy lid is the even pressure it produces across the whole hatch.. Having said that, the biggest part of beating the leak isn't so much the mechanism for securing the hatch. Weather its internal or external, most any mechanism will hold the lid down this. The LL does so very well.
The bigger part of stopping the drips is making sure the gaskets and gasket walls if you have them are bomb proof.

There are several ways to make gaskets or gasket systems that will compress to something water proof.

Good luck!
!RUSS