The carbon steel main camper trailer frame, odds are high it was MIG welded. All the ones I have seen have been MIG'ed. On mine, I have the wire hanging out of the weld when it stuck on the welder to prove it...
The aluminium, I do not know. I have not yet seen a Sunline aluminium wall or floor unit up close and personal to tell.
On the wood floor/structure campers, yes they used carriage bolts to bolt the floor down to the metal trailer frame. That works well on day one. After many years of rusting on the bolt heads under the camper, they get rusted up badly and the square under the crowned head just strips and spins in the wood trying to get the rusted nuts off. Granted this is not a common replacement item.... The only time they come out normally is on a rebuild. On these campers when this happens, you end up cutting the bolts off under the nut and pounding the bolt up out of the floor. 4 1/2" grinder with a cut off wheel works wonders...
Sunline was one of the better camper builders. They took the time to make them better in most cases. Granted these things are still an RV... but craftsmanship goes a long way in making them last longer. The owners need to understand the needs of an RV as well to make them last.
