We have 110v unit in our trailer. It's adequate, but no better than.
A 220v unit is much more efficient and can do better at raising water temps.
The most efficient are the gas units (natural or propane). I know to local plumbing companies that will not install electric units due to the large number of complaints that water will not get hot enough in the winter. Since we don't "winter camp" I don't know if they are right or wrong.
We are thinking about one when one of out tank units fails (we have two in the house). It will likely be the one serving the downstairs (kitchen, laundry, bathroom).
The Cabela's unit might be just the thing for a small barn as you can turn the gas on and off at the tank as required. Gas does a better job of heating and does not draw as much current.
I have one of the coleman ones and LOVED it until I had to recharge the battery. It won't hold a charge. Bought a new battery. It won't hold a charge, either, so it's probably something in the unit or the charger cord.
Bad thing for me is that I bought it (new) off ebay. Coleman will only deal with you on warranty issues if you've bought from a "real" retailer. I'm just hoping my nerdy boyfriend can rig something up for me that will work. Right now, I'm pissed that I've thrown $230 down the drain. If it worked, it would have been GREAT!