I can appreciate quality construction, but the question is whether glue and staples will fail. If not - it's a perfectly acceptable method. If it will fail, then there is value in a better method. Otherwise it's just wasted effort with no benefit. Either way it doesn't justify the price. Cabinets aren't particularly complicated items to manufacture.
I agree wholeheartedly. It is acceptable to use glue and staples and in fact, it is the standard in almost ALL travel trailer designs. Only time will tell if they fail. Although I have read numerous failures in "off road" designed pop ups and travel trailers because the staples would not hold while driving over washboard forest service roads consistently. If you're going to stay at campgrounds that have paved driveways, your trailer will last forever. I'm only speaking to those that want to actually take a trailer off the pavement. Cabinets are definitely not complicated to make. Its the installation process that makes the difference. Again, is it worth it to someone? Only the buyer can determine that.
The trailers are very simple. They are probably not engineered - at all. I don't think you can justify the cost of actually modeling the forces to minimize weight. There's no need for a single longitudinal frame member like running the tongue all the way through. In fact it would be a very odd engineering choice to add weight in that way with basically zero structural benefit. Again we're at the same issue - will it fail? What is the designed safety factor? If we're building them in steel - 2x3 tube with 18ga walls is more than enough. 12ga is probably overkill. A simple rectangle frame is basically all that they're using. They're all sitting on some version of a $500 trailer.
Again, there is no NEED to have a single longitudinal frame member. However, I know that a 2x2 steel tube frame at 15ft (tongue to tail) will have a 1/4" of deflection with a teardrop body on it. Is that significant, maybe not for someone that is just going to take it to campgrounds. What's going to happen to those staples once this thing goes off road?
Upgrading suspension should be easy for any trailer shop with basic fab skills. They weld on trailer frames all the time. They probably come with 1500lb leaf sprung axles. You can swap out a 3500lb axle with hubs of your choice for about $150 with new springs. I paid $180 for a full kit with new spring hangers and then narrowed it to suit. Then put larger tires on.
If they're torsion axles it's even easier. You just choose a different angle torsion axle and bolt it on. Add some spacers if you want.
I didn't get into the details of changing suspension because you're right. It isn't difficult to add leaf springs if a trailer started with torsion bars. That is the simplest way to upgrade the suspension. However, in order to modify the frame for Timbrens or air bags would be very challenging. The mounts for the Timbren style require the frame to be wider than designed. I've seen some people just weld a plate so that the Timbrens have a place to bolt onto. Will it work? yes. Will it be durable? Who knows in the long run.
As an aside:
I don't know why trailers stick with 1950's trailer bearings. I didn't get my prototype in for this trailer, but my next one will use off the shelf unit bearings instead of trailer bearings. I have two sets I've been engineering adapter plates for - GM 1500 front 2wd 6 lug sets, and rear Highlander sets. The plates will match the OEM bolt plate on the spindle and you will then weld that into your trailer axle tube. Have a bad bearing? You can guy a GM 1500 unit bearing at any auto parts store anywhere. No messing around with trailer bearings and all the nonsense that goes along with them. And it's 4 bolts to replace just like any unit bearing. (GM only uses 3). Never have to service them. Never have to grease them. Never have to repack them. They just work.
Absolutely agree with you here. But the bearings used ARE off the shelf units. The Timbren 3500lb bearing assembly uses the same bearings on a 1 ton chevy. Not the sealed hub/bearing assembly found on 96+ GMs, but the same repackable/replaceable bearings before then. It would be more convenient to use a hub bearing style and I'd like to see those more often. Especially since they won't see the daily use a front end of a GM truck would, I imagine they would last quite a long time.