I trust you've tried running with the seat up -- just to see.
We've had two "Heart" a/k/a Xatrex (now) inverter/chargers over the last 22 years on two boats.
They have worked fine. Had one warranty issue, they simple replace the inverter (that was about twenty-one years ago -- probably an installation issue, but they didn't quibble with the professional installer who sold it me).
Xantrex has gotten some bad press, including here, BUT for me, their product seems to have performed.