Many of us 2-part epoxy to fill and stabilize voids or cracks in wood. In my case I work with a lot of figured and live edged Big Leaf Maple. Often there are large “defects” and/or voids, such as burl inclusions and insect trails, that need to remain visible to maintain that particular objects character.
I use a clear pour-on resin that is used for bar tops or tabletops. I can even use dye in the mix if needed. After 24 hours of cure time the filler machines and sands very well. I simply mix the coating and pour it into the void. If the void or crack goes all the way through a piece I put masking tape over the hole on what will be the backside, to seal it up, and make the pours from the face side. If I am not sure which will be the face side, I do the same process before final milling to thickness and then run it through the surface planer to final dimension.
Even if you need to add more filler to get the final result you are after, the subsequent pours are invisible. I even use it in combination with epoxy or “Super Glue” since they are basically the same type of resin and can be used to “seal” a void in a shorter period of time and then fill with the pour-on product. When top coated the fill is completely invisible. The result is time and temperature stable and costs far less that epoxy. I have several tables that are years old and the filled areas do not change.