I don’t think you -need- a tumbler. I bet you can do it passively with about 6" spacing for like 1" pvc with holes in it about 3/4 up and capped on top, you wouldn’t need to tumble. You really just need air circulation and some low grade heat. The problem with chips is they can get packed too tight and there isn’t enough airflow and it will create tunnels. With a tumbler you are stirring them up, the passive way you are just distributing the air. The tumbler will be guaranteed to be more even and faster. but more energy input.
Then you can probably use like a “solar air collector” for low grade heat if you want/need to split the systems apart. IE you want to dry but don’t have an immediate use. it is similar to the solar grain bin driers. You drop the moisture content from 25% down to <18% to prevent molding and starting a fire, then you can finish it off with the tumble drier if you need to.
You -might- be able to do the passive system without a fan if you can get it to draft a bit. It doesn’t take that long to dry out green brush sticks just packed in a 55gal drum in the summer like a day or two, with the lid and a nipple in the hole and a draft aid. It is essentially turns it into a solar dehydrator. I was thinking a couple of 4x8 sheets of foam insulation for panels with plastic over it but Here is a fancy dehydrator: