I have used the couplings on double-wall culvert. (To attach a saddle-tee for a pipe connection.)

The couplings themselves a fairly leaky. However, I think the coupling would do a good job of protecting the sealant that you applied over the gouge. I think your plan should work - unless the gouge is very deep relative to your normal water level and it would be subjected to lots of water pressure.

Good luck on your fix!