I've heard of people using plywood to move tanks with substrate still in them, but I've never done it personally.
Don't leave any water in the tank if you're gonna do it though, drain it as much as possible and just cover the plants with cling wrap to keep some moisture in.
If there are fish just put them into buckets, along with the media.
Trust me though, a 20 gallon with just substrate is INSANELY heavy. I drained mine completely of water when I had to move it in a rush (long story, the room flooded basically and I had to take all the furniture out.) and it took 2 people and a lot of swearing to move it to another room. It didn't crack or snap thank god, but I think I just got lucky.