A few questions for you kats with Magma (or similar) grills:
1) SpoilsofWar, do you leave your grill mounted when underway, or bolt it up when you're on the hook and want to grub?
2) Do they collect a fair amount of junk, like burnt food, ash, grease, etc.. that would make removal and stowage inside the boat messy?
3) Any concerns about grilling over expensive-to-replace vinyl seats, or near 120+ gallon fuel tanks?
1. I leave mine mounted at all times. I've never had any issues with doing this, and I've been in some bad storms with it. It's been mounted just like you see in the pictures since early 2012, and only removed for cleaning. If you go to the Magma website and look at their vast array of mounts, the specs list which ones they recommend for use underway and which are supposed to be stowed when underway. I'm not even sure which mine is rated for, and at this point it doesn't matter to me because it just plain works.
2. I think the answer to this question depends on the style of grill you get. For my kettle, depending on the type of food cooked, it will collect grease drippings on a plate below the main kettle, where the Venturi gas tube passes thru. Mainly this is with fatty things like hamburgers. It's not excessive, but this is one of the reasons why I swing the grill out over the water when it's in use (the other being that it gives me room to sit next to it and work the grill). I clean the grill by simple hosing it out every now and then. Being stainless, you won't harm anything. I'll even admit to completely dunking it in the lake when I wanted to clean it during a camping trip.
3. As long as you have some clearance (I would say no less then 6"-8") between the grill and vinyl, you will be fine. You can see the proximity between my grill and the vinyl covered sun deck... The vinyl is unaffected. What you can't see is that it's also about 18" from the engine compartment blower outlet (on the port side hull under a cowling) and about 3 feet from the gas fill port. You're using this item outdoors, with fresh air circulating all around; it's not going to blow you up. How close to the gas tank could you really put it, anyway? Some people may say this is dangerous, but I have 4+ years of empirical use to back me up saying it isn't. Now, I wouldn't recommend grilling while you fuel the boat and run the blower, while simultaneously smoking a cigarette, or any other potential Darwin-award winning actions. But you're gonna be fine in normal use, just like all the other boat grillers I see on my lake.
Hope this helps.