I'm wondering whether there's any drawback to this approach, and especially whether it would work even after sprouting until the seedlings reach the height of the dome — or whether that would encourage damping off. I'm hoping others on this forum will have tried something similar, or will have thoughts on the idea.

I think that leaving seedlings under the dome for any period of time would invite problems like damping off. I use small domes to stimulate germination and emergence but as soon as the seedlings emerge I pull the domes and turn on a small electric fan. The artificial wind from the fan is beneficial to the seedlings, makes them sturdier, and keeps excess surface moisture from breeding damping off. The air circulation also gives the plants better access to carbon dioxide in the air.

I add a small amount of BT (bacillus thuringiensis) to the water to control fungus gnats. I use a urea-free nutrient formula to avoid a potentially harmful buildup of urea. I use melted snow or rainwater to avoid salts buildup in the growing media (Premier Pro-Mix BT). I overdrive my fluorescent lights for higher light output.

MM