Depreciation is just about bottomed out at 10-15/years. Best age to buy one as that’s a trailer “better” in used condition (design & construction) than the plastic white boxes churned out as fast as possible.
The 2013 boxes are about ready for being removed from the road. 70k mile lifespan, more or less
A/S and its upmarket cousins no longer in production are quarter-century before refurbishment (as needed), and 250k mile lifespan (before major work).
If RV’ng isn’t a great number of miles annually, then a box with slide-outs is okay. If long-term ownership and long-distance travel is the thing, get the trailer built for it.
As to “space”, just how many interior cubic feet do you intend to hear or cool? How much work do you want to do in cleaning? Repair & refurbish?
I’d have chosen a 27-28’ as that’s the best opening size for full-time travel (capacities) given that inclement weather or being ill can leave one confined for days. Not any harder to tow, or to back.
A 22-24’ has the advantage of more TVs that can be used. Full independent suspension and short rear overhang and better power-to-weight ratio means a better highway rig. If the bed of the pickup is just some storage that could be done elsewhere, then living with a better TV design is easier travel (past greater highway stability).
AIR forums has a decent amount of info on most subjects. “Tech” is generally better, here (past A/S particulars).
Disc brakes are a strong recommendation for any TT. ZANETTI and others do installs (TRANSWEST in CO, another). GCinSC has an excellent write-up. Same for experience by guskmg. 4-whl TV disc plus TT disc is — as with big trucks — a whole other world.
Downgrade control and breaking forward momentum is what matters. Not speed on an ascent.
An early 3rd Gen or previous CTD is a good pairing. 15-MPG is what I average with my 35’ Silver Streak in the south-central USA. Consistent comps with more than a dozen others pulling 28-34’ A/S. One can break into the low 20s with a TurboDiesel car or SUV given a 22-24’ A/S and the desire to keep fuel burn lowest (some planning; some new habits).
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2004 555 CTD QC LB NV-5600
1990 35’ Silver Streak