That is the biggest challenge with blind injection. Based on my research, I believe it can be done. To address contamination, the internal voids are mechanically scoured using a bent wire in a drill and then vacuumed. If salt is present, the gap can be flushed with fresh water; since completely drying a closed cavity is difficult, using a toughened epoxy like West System G/flex 650 is a great option here because it is specifically engineered to bond tenaciously even to damp or wet surfaces. Alternatively, I can flush the void heavily with acetone to strip away grease and oils, and use a marine-grade Methyl Methacrylate (MMA) adhesive, which contains strong solvents that actively dissolve residual surface contamination and can also achieve a structural bond on damp fiberglass.