We had our LBS order a Swagman 64650 Cross Country XC
carrier for us. It holds 2 bikes with the option to carry 4 with another module, and fits our Class 3 (2") receiver hitch. Their 64665 XC4 Bike Carrier
looks like our 64650 Cross Country XC , but it carries up to 4 bikes. Hmmmm...not sure what the difference is between the two carriers, unless the XC4 is just the XC already equiped to haul 4 bikes. Swagman's also offer a ball mounted style which carries 4 bikes, but from looking at the pictures, it appears to me like the bikes might touch each other. Perhaps someone else has one, and can comment.
I can tell you that our carrier is light weight, sturdy, and the *wheel wells are adustable* to accomodate various size bikes. The rack is easily removed from the receiver, folds down into a small package for easy storage. And, if my memory serves me right, our rack will also fold up against the back of the truck.
We initially purchased the carrier to haul 2 Giant Revive semi-recumbent bikes, which are *heavy* bikes (were 42 lbs each). Now we use it to haul 2 RANS Fusions instead. Both the Fusion and Revive have long wheelbases, but as mentioned above, the tire wells are adjustable and will accommodate many style bikes.
URLs you may find helpful:
Swagman's main bicycle carrier index.
This is to the Swagman *64665 XC4 Bike Carrier* model mentioned above, which handles 4 bikes.
Thule also carries a similar 4 bike carrier that you may want to check out as well. I don't know anything about them though.
Anyways, hope this helps.
EDIT: Checked with DH and the carrier *does* fold up against the tailgate when not in use, as well as folds up when removed.