JLS, what's your thoughts on the max size and weight of a 5th wheel to pull with a half ton?
Honestly I don't know that I would. We spent a lot of time RV shopping and the thing we noticed is every 25'+ RV geared towards half ton towing was making lots of sacrifices to cut weight. The great thing about the traditional 5th wheel is they are not trying to cut all of the weight that travel trailers are cutting.
That means heavier duty frame, suspension, and most importantly... finishes. We looked at a Cougar ultra light 5th wheel and it had some of the flimsiest finishes of any RV we looked at because they are trying to cut weight for half ton towing.
The most important thing to factor in when matching an RV and truck is payload IMO. I had a crew cab f150 with a 3.5 Ecoboost. It was rated to tow around 11k lbs, but it only had around 1750 lbs of payload capacity. Every 5th wheel we looked at had 1100+ lbs of pin weight. Add in a family of 4 and other crap and we were pushing 1800 lbs of payload. Every decent sized travel trailer we looked at had 800+ lbs of hitch weight. You do not want to get over 80% of that payload capacity in my opinion, the sway gets nasty at higher speeds and you end up driving much slower which adds to your travel time substantially.
If you plan on driving out west in the mountains and wind, I can't recommend a 3/4 ton enough. The crosswinds out here are brutal and even in a 3/4 ton with weight distributing hitch you feel it. Even more than the wind, coming down a 7% grade would be a nightmare in a half ton.
When I was still trying to keep my half ton, I was getting frustrated at how limited my options were. We wanted dedicated bunks for the kids and enough space to live in for a few weeks with tons of solar and batteries for off grid boondocking. It just wasn't possible.
I ended up getting a gas burner 250 and paired it with a 30 foot Airstream that has a twin over Queen bunk in the rear and a queen up front. I have 3300 lbs of payload and Airstreams are known to pull really well, but I absolutely feel it. Cruising down I-90 I'm June I had to choke down to 65mph in an 80 because of the crosswind. Passed a half ton with a similar size trailer doing maybe 45 mph with it's hazard lights on. In the RV parks, it's almost exclusively 3/4 ton and up pulling stuff.
All that said, if you are just running from Jackson to Starkville for tailgating and plan on keeping it below 60mph and really want a half ton and fifth wheel rig... Grand Design Reflection 150 series was by far the best I looked at during my shopping days. For a half ton towable travel trailer with dedicated bunks, I liked the Lance 2185.