Any good quality generator will do if it has the capacity for your load requirements. The main problem in this application is how to get rid of the exhaust gases - on land you just stick the thing down wind and there you are. You can't just plop it down on the floor in the cabin and fire it up, that may be lethal. Generally auxiliary engines are mounted and vented very carefully, as with any engine on a boat.
The normal rules and safety with mains level power apply of course - construction grade fused safety switch power boxes are useful, but only if everything is correctly earthed, and that is hard on a boat with the potential for big issues with electrolysis. Generators are always many times more dangerous than mains power because of the uncertain earthing - there are many campers killed every season due to electrocution.
Many portable generators have a stubby pipe at the muffler outlet - often with a mesh spark arrester fitted. This can be removed and a pipe can be fitted to this but you must never restrict the size of this tube to less than this outlet size for short distances, and at least half again that size if you are going more than a yard or so from the machine with your extension - this is to prevent excessive back pressure and possible overheating issues. Flexible stainless tubing is available from engineering suppliers, if you don't use some form of flex coupling your extension system will break or crack and that is not acceptable on a boat. I have used a horrifically expensive high temp silicon tube with great success, the cheaper high temp hoses just harden and fail after a few dozen hours. The generator must also be mounted firmly and securely with protection from spray and rain.
You will either direct the fumes up high or well to the back and low - as you would any exhaust. Don't underestimate the potential seriousness of this issue, it IS a matter of life and death for any one in a restricted space like a boat, and of course you have the care of your guests to consider. I use and recommend sniffer units be mounted in any enclosed boat, they are very effective and have saved my life (LPG) and those of my crew (CO) on more than one occasion.