We have the same truck :-)
I would buy a used fiver of decent quality. Your preferences and the technology will change dramatically in 10 years! We purchased a used, but in good condition, fifth wheel from Kansas RV Center. They made Hitchhiker fivers until recently.
You will still need to be a bit careful not to fall in love with a huge one We decided to buy a SRW and find a fiver with a GVWR of 15000 lbs or less. We have been full timing for just over a year in it.
Do your research before getting caught up in a sales pitch. Many sales people will tell you that you can tow anything and that most RVs are 4-season. Wrong!!! RVs depreciate, so don't count on trade in value as doing much toward the purchase of another fiver 10 years down the road....