Mine also bowed out but sat flush before i added the automotive style gasket. Had I known this I would’ve tried to position the wood piece it sits on inward more when I installed it. A lot of people use clamps. Mine doesn’t leak much at all so I just left it alone. There’s no easy fix. For mine I would have to cut out the whole wood piece that holds the gasket and reposition it.
The main reason I decided on the automotive clear was because it requires less maintenance over time, it was also less expensive and not as time consuming to apply. I used a gallon kit of speedokote with medium activator on eBay for $70.