We found that when we started out with the ramp going up into the truck or the trailer, our dogs didn't want to use it. We put it down flat on the living room floor, next to the wall and started having them get used to it by heeling next to us on the flat floor. It took a bit of time, but both our 13 year old Golden and our three-legged Lab/Chessie were able to negotiate the ramp. Now that they are both gone, we are planning to train our new two year old rescue Lab to use it, too. No sense in causing undue stress on those joints when we don't have to.
They also make a set of foldable steps for dogs to use (Petloader is one) and also a couple of companies (Otto Loader, etc.) that make a step that fits into the receiver hitch of an SUV.