The cover for the airbox on this Honda generator hinges open to the left, but the frame rail is directly in front. The airbox is also bolted to the engine from inside (behind the filter).
I've throughly looked over this and there is no way to open that airbox unless you unbolt the engine from the frame, or perhaps modify the lid hinges with a saw so it doesn't have to swing as far to come off.
Those hinges could be resecured with some L shaped pins not to different from how Chevy truck headlights are fastened or trailer hitch pins. Gravity will keep them in place during normal operation.