Actually, there are good quality, lightweight ex-pens and crates for large dogs too. Even more important as the weight
increases with the size of the dog.
We travel with two Rhodesian Ridgebacks and they are well contained in either crates or pens.
We also leave them in the trailer on occassion. If hot we run a portable fantastic fan.
Most important consideration for how to contain your dog is to know your dog. Some cannot and should not be left in a soft crate or soft pen. You also need to consider whether your dog is a chewer or jumper and how high they will jump. Or, alternatively, how well trained they are to accept containment. Mine can jump but choose not to.
We use the "It's a Breeze" brand of crates and pens for our two. They each have an appropriately sized crate and we have two pens that we connect together into one large pen. It has bases and mesh covers for added security.