Actually, I think launching players from the cannon might be a good alternative to vehicles. This is how it could work:
- When exploring, a player would deploy a target marker at the location he intends to return to. Marker is a special item that works similar to a beacon, i.e. it can be put on the ground, assigned a label, and picked up when no longer needed.
- then player comes back to base, restocks on ammo/fuel/health items
- when ready, he enters the cannon, selects destination marker and fires
- the missile travels all the way to the destination marker and opens in the air right above it, after that player safely reaches ground by using jetpack or parachute
The cannon itself should probably use a lot of gunpowder, and a reasonably expensive "missile" with human compartment. It will also work great in multiplayer to quickly summon other player from the base. Since it is one-way trip, the vehicles are still useful to reurn back to base.