1. The point of Hovercraft (the air cushion ones) is so they can travel both on land and the ocean. At the very least they should be able to enter the coast. Maybe something like this ...
Hovercraft = Land + Coasts
Modern Hovercraft = Land + Coast + Oceans
Hi-Tech Hovercraft = Land + Coast + Oceans
Because even today we have Military Hovercraft which can cross the ocean and then come up to land.
OK, you convinced me. I'll just give them higher maintainence costs to keep things balanced.