Hey, everyone. New to the forum.

Background:
I recently started looking for a preowned pickup truck for the road trip to tow the RV ( RV not purchased yet, appreciate if you have any experience about RV, too!)
I'm choosing between 1/2 and 3/4 ton truck, i know this is the question how much GVW and tongue weight is, but I'm open to get a larger RV( travel trailer or fifth wheel) for my family ( wife & toddler).

Question:
1. For preowned trucks, what's the year & mileage range you recommend? Since it's a trip circling USA, durability and reliability are very important to me.
2. Because I need to put car seat, so a crew cab is a necessary, Which model or trim you would recommend for my situation?

I'm super new to truck world, sorry for these silly questions!
Lei