Most of members here drive full size trucks with big TC on them, when sounds like you are focusing on smaller one?
So figure out what you really need
-bath? Wet or dry?
-big dinette (slide) ?
-AC ?
-how much storage?
-size of holding tanks?
When any truck can pull 4k boat, you will need to buy a truck and then a camper.
Did you think about Class C motorhome or ClasB ? They will come cheaper and easier to set.
When it comes to "no older than 10 years" rule some campgrounds enforce - they don't intend to turn good business away.
I was camping at several of those with my 30 years old motorhome. But it was Prevost, so go figure.