Biuddy,
Pumps like to make pressure, they do not like to suck, (sounds like my wife, in more ways than one!) so any help on the inlet side for the pump helps the pump work better. These include, large inlet lines, the bigger the better, and a little positive pressure on the inlet, which is usually done by having the pump lower than the fuel level. If you do a separate tank for the injector pump you will need to locate it close to the injector pump, and you will need to have a line that goes from someplace close to the top of the tank back to the main fuel tank as the electric fuel pump(s) supplying the injector pump tank should be at least 50% larger in volume than the injector pump which means that there will be constant flow of fuel from the injector tank back to the main tank. The injector tank will also need some sort of breather to prevent over pressure in the tank and also provide atmospheric pressure to push the fuel to the injector pump. I have always thought the best tank design is a tall cylindrical shape with the fuel pump inlet at the bottom, I would also suggest a baffle across the inside of this tank to prevent any possible swirling of the fuel. You may also consider connecting the injection system return line to this tank which will help keep it full and reduce the amount of plumbing back to the main tank. If you do run the injection return line back to the main tank, do not combine it with the return line from the injector pump tank.
A thought on the line size for the pump inlet. If the pump has a -6 or -8 inlet connection do not assume then that the line size should match that size. Buy a step up adapter from the -6 or -8 to at least a -12 line and drill out the fitting as large as you can. Even with the inlet port acting as an orifice it can be shown that the increase in line size reduces the pressure drop through that line substantially.
I would think that you would have someone fab the tank for you as you will probably mount it in front of the engine. Actually with the set up you have why don't you just make a 5-10 gallon tank to mount in the front of the engine and then skip all of the electric fuel pump hassle altogether. If you look at some cars that run big engine set back, link yours, you will see many of them have both the fuel tank and the water tank mounted up front to both help the water pump and the fuel pump.
Ice is not a problem at the salt, last year there were two semis parked on the salt with ice.
Rex