RVing with 3 children under 5

I don't know who rents tow vehicle/trailer combos. My impression was you were buying this time around. I've driven both Class C and tow units. The Class C has the benefits of not having to leave the unit to use the bathroom (when stopped of course) but 5th wheels are very easy to tow, offer lots of space and utility, and then you have a tow vehicle that can easily accommodate the kids, you, and gives you an extra vehicle (albeit a large one) to tour with. If you can find a rental agency I'd suggest renting one for a long weekend or just to drive to see if it's something you are comfortable with.