I use a fishing rod holder mounted on the rear rail. I have it mounted at a 45 degree angle, upwards to the starboard side. I then have a rod holder mount under a Magma Newport (rectangular) grill. It's worked ok for the past two seasons.
Here's a picture of the rod holder mounted on the rail:

Friends with kettle style have complained it's not large enough to cook food for more than just two people.
The only downside of my transom rail mount is the risk of grease dripping onto the transom as it slopes sternward. Thus I try to limit cooking to things not likely to create too much grease. This often rules out doing hamburgers for more than 3 people. But I keep a squirt bottle with water handy in the transom locker to squirt away any drips. I also have one with some Ori-Pine cleanser in it.
At some point I'm considering putting a table mount in the swim platform. The same sort of table mount as used in the cockpit and down in the cabin. I already have the parts, I just haven't gotten up the nerve to take a hole saw to the platform.
I've also considered putting the mount into one of the doors on the platform. Those storage areas only get used for storing inflatable lounge rafts, and they tend to get rather slimy anyway. So losing one of them wouldn't be a terribly big deal. I'd want to figure out some way to keep the door shut better than the latches on there now. That and the hinges might not be 'strong enough'. But given the past two seasons, and the fact that I never have the grill mounted unless I'm actually using it, there might not be too much to worry about regarding the 'strength' of the mount.
I've seen the rail option, at least in pictures. I've not seen it on a 358 yet, nor in person. A grill is a relatively heavy item, at least the rectangular one is. I wouldn't want to try keeping it mounted if the boat was going to be tossing through chop. The rear handrail definitely doesn't seem like it'd be strong enough to allow full-time mounting, as tossing motion would put a real strain on how it's mounted. The rail is durable, it's the through-hole mounts that I'd be worried about. So I wonder how the rail would handle having something heavier mounted to it. I'd rather have something with more stability in multiple directions. I'd like an L shape instead of just a straight line. I seem to recall there being a FW option for a rail that mounted at the corner of a platform. But, again, I've never seen one in person to get a feel for it's durability (or lack there of).