I have this pad on my mostly exposed 50 gallon fresh tank. Yes I would get the same again. 120v alone allowed the tank to freeze as temps got down to zero. Put the 12v on and we had water in a few hours. 12v current draw is not huge and your converter should be fine for the single pad.
Running a bit from battery power should be fine in transit as long as you plug in at the destination.
My waste tanks and pipes I stuck with 120v as the total 12v amps would have required a second converter to supply power. These three tanks are smaller and lower risk of issues if partially frozen.