I'm using solid wood to make a worktop/countertop in my camper van. It's going to have an undermounted sink, so I need to use something to protect the edge of the sink cutout from water. I have no idea what product to use and can't find a good solution anywhere.
Whenever I have fitted a sink (surface mount) I have always varnished the edges of the hole I cut for the sink to go into. So, any water that does get past the seal just tends to drip down instead of getting absorbed.
I would make sure the hole has smoothed edges and varnish, or equivalent sealing, as appropriate to prevent the edges absorbing water and bulging over time.