Stop drilling at the end of the crack can help prevent it from spreading. Using a fiberglass repair kit is usually a better long-term solution than Bondo or caulk, as it adds strength. Proper surface prep and sealing will help prevent moisture from getting in.

Remove the corner trim and apply fiberglass repair behind the crack for a structurally sound patch. Bondo has a product that contains fiberglass, which can be used along with regular Bondo for cosmetic repair.

Tape the crack with Gorilla tape or Eternabond to prevent water intrusion. Contact the manufacturer to identify the material, as not everything on an RV is fiberglass, which can affect repair strategies.

Stop drilling is effective. Consider using a Dremel to v-cut the crack deeper, then fill with a fiberglass repair kit.

A vee cut may not provide enough surface area for a strong bond. A better approach is to grind back and glass the area, ensuring structural integrity by addressing the crack from the backside if accessible.

Identify the cause of the crack; it may not spread if due to an impact. For repair, it is preferable to access it from the back for structural support. Use a two-part epoxy like MarineTex to fill the crack, which is sandable to match the surrounding area.

Use a quality fiberglass repair kit to fill and cover the crack. Sand and paint to match. Stop drilling will likely help as well.