A great alternative is to build wooden boxes that are deep. A friend of mine was once contracted to grow ginkgo seedlings and that's exactly what he used. You need to be careful when sowing however as sprouts of seedlings or cuttings can dampen off when are spaced closely to each other. So sow your seeds carefully, always run a fan, etc.

Dax

Damping off is cause by soil borne fungi growing in very moist or wet soil not because the seeds/cuttings are placed to close to each other. Using sterile potting soil and careful moisture control is the key to preventing damping off.

I just made a crate to try. That seemed like a simple solution. Thanks.

I use lasagna pans. They come with a clear lid to hold in humidity. I also use them to wintersow seeds outdoors. I don't mess with trays and little plastic pots. Once the seedlings have two true leaves, I set them out in the hoophouse and let them fend for themselves. Once the threat of frost is gone, they'll get planted directly from the pans into the ground. If they live, great. If they don't, it just wasn't meant to be. I will pot a few for friends and the plant sale I'm planning. Otherwise, I don't fuss over it much.

Wintersown dianthus has already sprouted.

For indoor cuttings, I built a cloning machine.

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For outdoor propagation, I use Janie's Easy Propagation Chamber.

I use paper towell rolls and toilet paper rolls. I cut them 2" which is half the legth of a toilet paper roll. I stack them in a flat, fill them with my potting soil mixture and grow my seedlings. It has worked well so far.