I prefer the ballasts to be in a separate enclosure. I don't like the extra weight in the hood. Regular core&coil MH
ballasts get hot enough to fry eggs so you don't want them in your hood. Electronic HQI ballast should be lighter and cooler but I still wouldn't want them in my hood. If you don't have room for a remote enclosure then I guess you don't have a choice. Ballasts that close to a tub of SW
sounds like a bad idea. I would worry more about corrosion than heat although if that's how they are designed it's probably OK.
Glad to hear you are not skimping on the lights. High intensity is the way to go.