Just following up on my own post -- I got MG Chemicals clear epoxy because they thought it should bond OK; it seems to, but it's a little more viscous than I hoped, and more importantly it doesn't easily wet the very smooth SLA plastic, even when lightly sanded, so I don't think I'll use it going forward. (West said their epoxy may not bond well with the SLA resin so I didn't try that.) I read that clear acrylic sprays probably aren't a great idea for this application. FlexSeal seems like it would be way too thick. PlastiDip -- don't know? I'm kind of at a loss for a product that might work here. But in good news the SLA resin (Somos Watershed XC 11122) is apparently quite resistant to water to begin with, so the coating may not really be necessary. I guess only time will tell.