Add Hrm pro plus for open water swimming?

Hi.

I have started swimming with my Forerunner 245 i pool.

Works well counting laps, hr, strokes and time. Found I had to touch the end of the pool when turning to get 100% accurate registration of laps.

I want to start open water swimming when its warm enough.

The hrm pro pluss is compatible with 245 but the swimming is not supported. As I see it the hrm pro plus register pulse, strokes an breathing, but the 245 does not support gps open water. If the hrm pro plus register strokes, pulse and breathing when swimming I could have the 245 in a swimming hood or drybag so it would be over water and register gps?

Is it possible to get that to work? Possibly with a custom activity. It would have to be able to upload to strava.

Thanks in advance Magnus.