Just wondering, why a rowing machine and not an elliptical ? Those exercise legs, arms and heart.

They are also cheap or free at times.

there was one down the street for free. I only needed to weld the one crank arm back onto the shaft.

I used it faithfully, for about a week, then it sat for 3 months, then it went to the metal recycler.

As for rowing, have you seen the 'Forward Rowing" set up sold by Gig Harbor ?
it is for a boat, but if it rains all the time there must be some water around somewhere.