I wonder if you have lost the ground to your boat that should be coming in on your shore power cord. To have both fail at the same time seems like an odd coincidence. The test button is an internal device test that is really just making contact between the neutral and ground.
Do you have an inverter
and if so do your GFIs still flash when that is operating and the boat is unplugged?
To further investigate I would make sure there is nothing plugged in to any outlets including battery chargers
, rechargable lights
Then, if you have a tester, or can get one, I would confirm that the ground is still good to the boat. If that is fine then the GFI's should be no different than one at the hardware store. Generally, cheaper GFIs are much more apt to nusance tripping than the more expensive (sophisticated) ones like Hubbel. Good luck. I'd be curious to hear what you find.