I believe Gil Gilpatrick mentions filling gaps with partially set-up resin. This would be rather easy to do if you follow this sequence: apply the seal coat thinly. Leave a little resin in your mixing bucket. Wait a bit for that remaining resin to start to set up, and use that to plug gaps. Once it starts to setup it should have sufficient body without needing any additional fillers. Or, you could mix in a bit of the sanding dust for opacity.

Hope this helps

PGJ