How do you encourage PCs to use an ATV to get to the adventure site (and this have those nifty animal encounters and such)...
I wanted to address this particular point, because I think it's an interesting topic.
In my view, and I only just realized this thinking about it, the animal encounters don't matter until they can matter.
That is, if the PCs can fly over the landscape in an air/raft and avoid animal encounters -- good for them! That's what an air/raft is for and if they have one they should be using it to do just that.
The animal encounters are there for when the the PCs might encounter animals. Sometimes the PCs will be in circumstances where they can dodge the animals, and other times they cannot. And that is fine.
For example, even if the PCs have an air/raft to travel to a destination it can be lost, stolen, damaged, and whatnot while they are out in the wilds. I'm not saying the Referee should work to make this happen, by the way, so he can bring the Animal Encounter tables into play. I'm saying that in course of circumstances it might come to pass that that the PCs no longer have the air/raft available to them. In this case the Animal Tables come out.
i know you are using Classic Traveller, and I think one of the brilliant things about Classic Traveller is that it provides the Referee with an incredible set of tools to support his imagination during play. But there will be times when certain tools will have greater impact than others. But when you need them ("Guys, the air/raft is shot... we're going to have to hoof it back to that last town and see if they have the parts we need...") then you have them.
Keep in mind as well that many of the encounters are flying creatures, some of which might cause a PC party trouble.
And finally (and I think I mentioned this over at the Classic Traveller G+ thread) but an Encounter doesn't have to mean "attacks the party." If an encounter is rolled while the PCs are flying over the landscape they might see a beast making its way to an unaware miner's camp, attacking a convoy, or pursuing some aborigines of the planet. In any of these cases the PCs now have a choice to get involved. In all of these case they now know something more about that the world (there are miners, there are caravans, there are aborigines) as well as a look at some of the beasts that dwell upon it.
I know Frank has seen them, but here is a post called
What We Mean When We Say “Encounter” on my blog about this matter. And here is another post called
More On the Value of Tables, Improvisation, and Lack of Plot which discusses how the tables of Classic Traveller help the Referee generate content on the fly -- which in turn generates adventure on the fly. (It includes ideas from Mike Wightman's posts here on COTI.)