I've used only wood. I've never used cinder blocks. You are right, they are way too heavy and bulky.
I always travel with a variety of lumber, enough for any occasion. When going to a new campground or even a new campsite in a familiar campground, you just never know what you are "really" going to get into.
Here's a good example of not knowing what to expect. If I would have used plastic Legos, they would have never stacked high enough. Nothing beats a solid chunk of wood. These blocks came out of a support beam from an old barn that was over 100 years old when I got the blocks. I've had these same blocks for at least 20 years now myself. Solid, don't rot, but yes, heavy! But the end result is a solid foundation under the camper. I give them a fresh coat of paint about ever 2 years or so.