The higher quality trailers have 16" O.C. floor cross-members. I've seen some cheaper ones with 18", but personally have never seen 24". Maybe they're mixing up the specs between floor x-members and wall/ceiling x-members? My Homesteader 18x8.5 enclosed has 16" floor, but 18" for wall/ceiling for example. What trailer GVWR are you shopping, perhaps that has something to do with it? Maybe the smaller/lighter trailers have wider x-member (due to less carrying weight).
I don't know what you're hauling, but my recommendation for a general car-hauler would be at least 20’ enclosed, dropped tail, tandum axles with electric brakes. Personally I would say go for 10k GVWR instead of 7k. That way if you need to pull a truck or 4x4 you have the capacity. Also I would install a WD hitch regardless of size and since enclosed add sway control.
Thanks for your advice. It ended up either being a misprint in the factory specs
, (I was reading under, "HAUV85X24WT3") or they upgraded to 16" OC for 2016. (the factory specs I found are for 2015 models, and my dealer had the 2016 year in stock.) I got under the trailer with a measuring tape and verified the floor is 16". I couldn't see the walls or ceiling, because it's all finished in white inside (which I like very much!).
My truck's window sticker says it came with, "TRAILER SWAY CONTROL," but the empty trailer was swaying a lot on the drive home, empty, so I'm not sure what this factory "sway control" is all about.
The trailer I took home is the 24' x 8.5' and has a V-Nostril, so I've been wondering if there's even room to use one of them WDH's on it. It's a 10,000 lb GVWR, with dual #5,000 axles with electric brakes. It's an all aluminum Haulmark, the "ALX" enclosed model. It seems pretty nice.
I also looked at a 24' Featherlite GooseNeck, that had its floor x-members on 12" centers, pretty beefy - but it was built in 1999 and a little too beat-up for my tastes. The FeatherLite was rated for 14,000 GVWR, and surely would have towed like a dream, but it was a couple grand more expensive to boot. I just couldn't swing it.
My new Haulmark does have the internal beaver-tail, screwless exterior (only 0.030"), all LED lighting (including switched-on-the-wall interior lights), 14" roof-vent, plus two corner vents, RV-style (camper) side-door, so I can sleep in it without worrying about anyone locking me inside, or knowing I'm in there (no windows), fancy aluminum wheels (got a steel spare), but it's got 3/4" DRYMAX (looks like particle board to me) floor, and 3/8" DRYMAX walls (presumably under the white vinyl interior finish). How's the water-resistance of this DRYMAX stuff, compared to good-old-fashioned plywood? Should I paint or coat the underside with something?
The aluminum frame is impressive underneath, and even the welds look very nice. It's got a very beefy tube-frame, compared to the I-members of the FeatherLite. It's not one of the super-premium brands, but it's a brand that's been around a while, so I feel secure about the six-year warranty (3-year bumper-to-bumper) it came with.
I was considering a "no-name" brand, to save money, but fell in love with this ALX HAULMARK when I saw it. I really like it a lot. By FAR the nicest trailer I've ever had (I currently have 3 other small trailers - but plan on selling all or most of them now). I've never had such a capable truck before.
Here's a picture of it at the dealer: