Moving pets across country, need moving van?

My boyfriend and I are moving from Illinois to Oregon in a few months. We are trying to see what our best options are. We've already decided we are going to sell pretty much everything to minimize the costs of a moving unit. But our dilemma is that we have a dog (about 55 lbs) and two cats that we are also moving. I have a 2 door Chevy Cavalier that we are taking with us. We were planning on pulling a small U-haul trailer behind it and just keep the pets in the car with us, all of them in pet carriers. I was hoping to rent a large van and pull the car behind us on a trailer so we could load our stuff in the van and also have plenty of room for the animals.

However, I have been unsuccessful finding a cargo van for rental use to drive across the country. I've tried U-haul, Penske, Budget...I feel like someone should have a cargo van for that purpose. Or are they mainly for short distances?

Any advice or links would be great.