After muxing around with all this for about a week now, I've decided to completely change all of my cooling ideas except for the large heat sink and water cooled plates, tubing and pump.
The 5 Gal. barrel is made of carbon steel, and was not 'lined' which means it would rust. So I put some Flex Seal all over the inside and that seems fairly decent, but I have concerns about Flex Seal 'sluffing off' or some residue from it getting through the rest of the system.
Another issue is that the bulkhead adapters I bought just don't seem secure enough in the thin gauge metal wall of the barrel. My first test of just filling the barrel up with water and leak checking with no pressure failed. Granted that was just a leak on the outside thread side of the bulkhead adapter, but basically this is all just starting to feel too flimsy for a system that simply CAN NOT LEAK.
If it was to leak, several bad things would/could happen. 5 gallons of water would pour out over whatever it could (electronics, 240vac, 50vdc @ 200amp, wood floors, amplifiers, etc). This is a system that CAN NOT FAIL. By that I mean if it does fail, catastrophic things can happen.
So...I'm going to do this differently.
I think I'm going to start with a different reservoir. I'm considering a 5 gallon FUEL CELL. These use -10AN fittings. So no Bulkhead seal to leak. And the container shouldn't rust since it's made of aluminum. These are available on Ebay from $65-100 depending.
I'm not going to use the radiators I bought either. They're just too small. I thought they'd have 1/2" mouth's on them but they're 1/4" so way too small for the water volume I want to push through them. I just really didn't like the construction of them either, but thankfully these were cheap on Ebay so no big loss there.
Instead I'm going to use an ATV Radiator :-) These are about the same price once again on Ebay as the two Rad's I bought that aren't going to be used. And it can handle a lot more volume. These are about 16.75" wide, and 12" tall and about 1-2" thick. They have 1" barbed hose ports so big enough, but not too big. Though enough to be on an ATV then it's probably tough enough for sitting in a Ham Shack. :-)
And I'll probably get 4 each 200mm fans (2x each side of the Rad). These are $14 at NewEgg and they're quiet at only 800 rpm but they can move about 130CFM each.
It'll be about a week before I can budget for this change, so I'll write more then.