Took ages for the silicone sealant to fully cure. I tested the helmet in the water tank, and it's 100% airtight. That was a pleasant surprise, I expected to have to add dabs of silicone here and there to seal spots I didn't get the first time, but no. Other than being messy (a lot of dust and crap got stuck to it while I was working with the sticky silicone) and needing the paint retouched (bits came off while working with the sticky silicone, that shit gets everywhere) and needing weights, it's ready to go. That's maybe 15 minutes of work, once I have the weights in hand, then a few hours for the paint to dry.
It doesn't look as nice as any of the consumer models, but then it's cheaper by a factor of 50 and it looks better than any of the DIY helmets I've seen online. I'm very pleased with how this is coming together and I can't wait to put it to use.