When you run the numbers the 5th wheel of comparable size will typically work out cheaper.
For $50k, you should be able to get a truck and trailer in the 5-8yr old range both in good condition with years of life left in them of equal or greater interior living area (remember to subtract 5-8' off the class A length when comparing to account for the cockpit area eating up living space.
Remember with the Class A, you are going to want a car that will eat up $10-15k if of similar age and condition.
Also, remember as full timers, you don't have to put in 16hr driving days like folks who have a 2week vacation and are trying to burn thru 4000miles to get to a destination. We usually cap our driving days at 2-3hrs 2-3 days per week when traveling, so the need to go to the bathroom or make lunch, isn't a big deal.
That said, either will work in the end.
As someone else mentioned, huge step to go from no RV experience to full time with teens.