The chase vehicle

We're going to have a chase vehicle for our gear.  The reason for this is really a matter of time constraints.  I'd love to have the time to strap panniers to a touring bike and take my time crossing the country (like the guys I met in Kentucky when I was in 6th grade); but I have a wife and two kids and I can't afford the time.  My wife is extremely supportive, and will be doing all of the child care for our four and two-year-old girls while I am on the road--she's a saint.  Plus, I'm going to miss them.  So, I'd like to finish the ride in 5 weeks.

We're going to need to get the chase vehicle soon.  We're looking for something that seats at least 5 people and has enough cargo space for our gear.  The gear will include two small tents, a cooler, tools, spare bike parts, camp stove and clothing.  We will have to fit it with bike racks to hold up to 5 bikes.  Ideally, it would be diesel and we would run on used vegetable oil whenever possible.  That way the the riders and the vehicle would be biofueled.

The plan is for one person to drive while the others ride, swapping so that each person drives a portion each day.  We will meet up with the chase vehicle several times each day to switch drivers and fuel up with food and water.  This also means that the chase car isn't too far away for support if there is a mechanical problem that the riders can't fix on their own.  I plan to ride 90 miles each day and drive 30, so the group will advance 120 miles a day.  Does this mean I'm not riding the entire distance--yes--I'm only really riding 3/4 of the way across the continent.  So how do we decide who rides up the mountains and who rides down?  I'm not sure yet.