Why not contact Honda directly and see what they have to say about using a gasoline powered portable generator on a boat?
Fair question, but my guess is they'd not recommend it.
When I researched using one a year ago I ran across a post on Cruisers Forum which referenced Honda marketing on their website which included "Marine" use and some sort of photo or part of a video which depicted the use of their generators in that environment. The link is now dead and I can't find any reference to "Marine" use on their website for the EU2200i (maybe someone else can).
Add to that a few excerpts from their manual for that generator, and it starts looking like Honda would advise against it:
"Using a generator or electrical appliance in wet conditions, such as rain or snow, or near a pool or sprinkler system, or when your hands are wet, could result in electrocution. Keep the generator dry." (Even under a bimini most rainstorms are going to get the generator wet)
"To prevent a possible fire, keep the generator at least 3 feet (1 meter) away from building walls and other equipment during operation." (Problematic, to say the least, on a boat)
"Operating this generator less than 3 feet (1 meter) from a building or other obstruction can cause overheating and damage the generator." (This is in the section on conditions which would void the warranty)
"Exposure of the product to soot and smoke, chemical agents, bird droppings, sea water, salt, or other corrosive environments" (Also in the section on voiding the warranty)
Regardless, I know a LOT of boaters have accepted these risks in order to get the benefit from the generator (I'm one of them).