It sounds like you've got things figured out pretty good. I wonder about a sup-pump though. That sounds a little aggressive. Beside, a sup-pump has to be dropped into the tank. So, hopefully, you'll sanitize the pump, inside and out, before you do so. Plus, the electric cord, which will also be in the water.
Here's my solution for hauling water when we are on a campsite that does not have water on the site. The 35 gallon tank came from Tractor Supply. They do make bigger ones. The water transfer pump came from Lowe's. I recently purchased a new one (identical), since the one in the photo below is nearing 10 years old and has pumped, probably ... a million gallons of water (Ok, I'm exaggerating a little on that!)
The water transfer pump is 120 volt AC. I do have a 400 watt inverter I carry in my truck all the time. So if AC electricity is not available, I can always plug in my inverter and use it. I also have 2 Cummins Onan P4500i inverter generators. If we know we are going to be without electricity, we always have them with us. So, if push came to shove, I could fire up the generator and use it for an AC power source too.
Anyway, this works for us. The initial cost for the tank and the pump was well, well worth it. Just thinking about dropping the sup-pump into your water barrel sounds horrible. We have a hot tub and I drain it that way, since the tub is inside the house. I run the hose outside the door and into the yard (we live in the country, no problem with any nearby neighbors complaining about anything). Even though we use the sup-pumps for low spots in the yard and around the property, dropping it into the hot tub always makes me cringe. I simply cannot imagine dropping one into water you may end up drinking!
Purchase a proper transfer tank and pump, and do it right! You'll be using it a lot.
Here's a photo of the first time I filled the tank and tested out the transfer pump. I also sanitized the tank at this time, and this was a great way to sanitize my garden hoses, and this is also a great way to pump sanitized water solution into your fresh water tank in your camper, and then pump it through all your lines and let it sit a few hours to sanitize your entire system.
