I took this to a PM to Jim so it wouldn't be a bunch of off-topic discussion here, but I have received several PMs asking about 5th wheels. After decades of RVing, in everything from campervans to diesel pusher motorcoaches, including 6 years with a NuWa HitchHiker 5th wheel, I offered an opinion on brands, etc. While I did mention my opinion on specific brands to Jim, I will be more general here, and offer other suggestions.
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There is more to picking the right 5th wheel than just the brand and layout, especially if your friend already has the truck. Pin weight (the weight carried on the hitch in the truckbed) is a big factor. Some manufacturers use a heavy pin weight to compensate for lightweight axles and tires. Finding a balance is the key. Like your friend, we already had the truck (that we bought to tow our CD-25 boat)... we made our 5th wheel selection based on what the truck could handle. Heavy doesn't necessarily equate to quality.
Just like with boats, there are RV manufactures who make the good stuff and there are those who are building solely to a price point. Some of the brands that we considered full-time or extended living units (7 years ago) were: NuWa HitchHiker, Excel, Carriage, Teton Homes, and DRV. Of those, only DRV is currently still in production. Finding a good, clean, used late model of any of these would be good. Staying with the boat comparison, the number one selling 5th wheel is the Keystone Montana line... I would equate those with Bayliner boats, and that is not meant as a put-down. They sell a lot because they have good floorplans and they are built to a price-point. At the risk of hurting someone's feelings I won't list what I think are lesser brands. Look beyond the "flash" of a pretty interior. Some RVs are over-loaded if you put your stuff in them, and fill the water tank - not a good situation.
One RV salesman I talked with when we were looking to trade our HitchHiker asked how many miles we had on it - I guessed "around 45,000 - 50,000."
He said, "Don't ever tell anyone else that - these 5th wheels don't last more than 25,000 miles at best. We sell 'em, I know this for a fact." I don't doubt that "fact," considering the 5th wheel lines they carried. A quality-built unit, well cared for and maintained, will be good for many years.
Even if your friend isn't going to live full-time in it, you want something built to last. Like a good hull with a boat, that means a solid frame and good suspension under a 5th wheel. And, a quality-built "home" on top of that. When we visited the NuWa factory in Chanute, Kansas, I knew that was the 5th wheel we would buy... well-made, attention to detail, quality components, and a great service department to back it up. They are the only RV manufacturer that uses Blue Dow Foam for insulation, instead of the more typical white stuff; it does not absorb water. They have a roof system designed to keep condensation (and moisture inside an RV is a concern) to a minimum. This makes for a more comfortable unit while you're living in it, AND longer lasting.
When people are boat shopping, I recommend walking through some marinas to see what appeals to them. Same with RVs - don't just go to the dealers, walk through some RV parks. RVers, like boaters, are generally a friendly bunch and willing to share their experiences. Talk to the people who are really using them, not just the weekenders.
The truck is a very integral part of the 5th wheel experience. As has been said already, you want to have enough truck to comfortably do the job. With a heavy pin weight, a dually is going to be necessary. See what kind of trucks people in the RV parks are using to tow any particular brand/model. With a pin weight in the 2,200 range, a single rear wheel truck is up to the task. A quality hitch, rated for the load is also a must. When we bought our 5th wheel, I thought I should have a sliding hitch - the dealer said, "If you need a sliding hitch to get into or out of a situation, you are putting WAY too much stress on the suspension of the 5th wheel." Turns out, he was absolutely right. In all the time we had the HitchHiker, a standard hitch did the job fine. And, while speaking of hitches, the HitchHiker we had used an articulating pin box (on the front of the trailer) - it rode quiet and comfortable; none of that jarring "back and forth" motion we have seen with some hitch/pin box combinations. Makes for a much better travel experience.
In another comparison, Ranger Tugs uses thrusters to make the docking less stressful. A set of hydraulic jacks under a 5th wheel will definitely make set-up/leveling less work and stress... especially if your friends are traveling a lot. (Some people use their 5th wheel as a "winter home," and only tow to get to and from the warmer climate.)
We were not full-timers while we had our HitchHiker. We divided our time between the 5th wheel, the boat, and occasionally our home. We definitely spent more time in the 5th wheel and the boat, than the home. When we traded the 5th wheel for our current motorhome, it still looked and functioned great. The quality materials (good carpet, nice woods, Corian® countertops, etc) showed very little wear.
Like the Ranger Tug factory and Wefings in Florida, a good place to start to find a quality 5th wheel would be Kansas RV Center in Chanute, Kansas. Yes, they are the former NuWa factory folks. They sell good brands and refurbish HitchHikers. Same service people. See what brands they carry.
There are pros and cons to every type of RV (again, like boats: cruisers, fishing boats, ski boats, etc, etc). I have heard people at RV shows rave about the "good price" on a particular unit, not considering how it will hold up or what the resale value will be, down the road. Just like a Ranger costs more than a similar size Bayliner - and there is a good reason for that: how it will hold up, resale value, good service after the sale, and the most important thing: how it will "live" and function while you are on it.
Travel trailer, toy-hauler, 5th wheel, motorhome (Class A, B, C), truck camper - lots of options. Also like a boat, there is a learning curve with any RV. Escapees (an RV owners group) offers a "boot camp" to get people up to speed faster and with more confidence.
Good luck to your friend as he makes the decisions,
Jim