before you jack your generator up on a platform, you need to consider how wide your boat is. I would not recomend doing that for any boat that is narrower than 56'' at the BOTTOM. a boat with any narrower of a bottom will become unstable unless you have a really small generator.
Like others have said, just place them in the rear of the boat, and like JP said, if your boat is small, do not bolt it down. Being able to shift that weight around will help keep balance which is the key factor to smaller rigs.
Also, why on earth would you mount a generator up in the air anyhow? I mean, if I were in a boat that did not have a fan, I dang sure would not want my generator to cause clearance issues and keep me from going up in some tight spots. you can work small troller rigs into some thick chit, but you cant with a hunk of metal and a generator hanging up over the outboard.
no offense twards you guys that have done so, but its obvious you guys do not need to work your way up into thick timber too often...