When you get to Chanute, ask them how those older units were built. The blue Dow seems to be something that has just come along in the last 10 years or so - just an impression I get. They used to use fiberglass in very old units (tan siding).
When I toured the NuWa factory in 2009, they showed us a black frame they said came from across the street - south of the factory next door. Was told all their frames come from that weld shop.
Any trailer needs to be inspected around all the outside joints starting after the first season. The old putty seals were absolute garbage - luckily, I haven't seen much of that lately on the newer units at the home park. Most use some kind of non-silicone "silicone type" sealant. Dicor maybe?? Most will start to have very small hairline 'cracks', usually near the end of a joint, starting after just one or two years in some cases. What is critical is to stay on top of those, cleaning out the old sealant and re-sealing before water gets in too long and does a LOT of damage.
Front and rear caps where they meet the rubber roof are prime candidates for sealant cracking and needing repair. This can cause major roof situations. (How many trailers have you seen going down the road with a big 'bubble' in the front of the roof where the rubber came loose from the roof? I see a lot!)
Another thing to look at is the slab side to see if there is rippling or any other sign of disbonding of the fiberglass shell from the luaun it is connected to. If so, there was probably water in there somewhere. When luaun gets wet and water wicks into it from any little leak (seal leak mentioned above), then it goes to the consistency of toilet paper, and with that failure, the fiberglass is free to move around.
Examples; I have mentioned my old worn out 1997 Kit Sportsmaster. Got it when it was about 9 years old. Neglect had caused much failure of the seals all around the unit. I have steadily and carefully 'fixed' each seal with dicor and no further leaks are happening now. The problem is that each corner of the trailer has rotten wood. Can push the inside wall with a thumb and it goes right through the rotten luaun and will crush the rotten corner studs.
One other thing - some trailers (cheaper) have the same type fiberglass sheet up the front rather than a hard shell cap. There are two, one an Outback, one a Sunnybrook at home park right now where the luaun got wet, failed as above. Large ripples, two and three feet long by 18" wide are visible on the front. One of the guys (2001 Sunnybrook) is looking for a house so can move out. Said he plans to just give the trailer away since the front has that going on, plus some rot in rear corner wall. All from leaks where the failed joint seals got away from him. (I told him I would buy the trailer from him for cheap, but he says no, he isn't going to take money from someone for it. )
Anyway, what it all boils down to is that older can be great if it has been cared for, but you really have to keep on top of it!! From day 1. Don't get caught up in the "looks" of a repaired joint - it seldom will be as pretty as factory - just make sure you get the leaks as soon as possible. There is continuous ongoing vigilance required to these things.
Arctic Fox advertises in their brochure that side walls are R-7 insulation. That don't seem so great to me.
Attention: TDR Forum Junkies 
I guess you could throw them in a box if you were worried about breakage. I'm guessing a rear kitchen would be a little heavier in the back? I could see that being a big problem on a bumper trailer but maybe not so much with a 5er.
