It's not too common, but it has happened to some trailers. I'm not sure about Scamp
frames, but Casita uses a pair of 3" mild steel "C" channels for the two main frame rails. Generally if there is a frame problem it will usually be in the vicinity of where the frame rails are bent inward, at the front of the trailer shell, as they form the trailer tongue A frame. Those bends create weak spots in what I would consider an already structurally undersized frame. That area would probably be where you would find any cracks, if there were any.
As old as your "vintage" Casita is, it wouldn't hurt to get a rolling creeper and visually check the whole frame. It has probably seen some wear and tear in its 20+ year life. Since your trailer was built in the early days, when they still welded the axles directly to the frames, that would be another area I would check over well. Later model Casitas have their Dexter axles bolted on now, which makes them much easier to replace.
Another point to consider is also that your axle
is well past its prime. Due to it's age, you probably have lost most of the suspension due to deteriorated rubber in the axle
, and may want to consider having a new one installed. For a couple of hundred bucks, you can have a new one installed at any horse or utility trailer repair shop. They do them all the time.
Here's the axle
specs that Casita uses. (If you have them cut the old axle off, and while it's off, have them weld a couple of 1 1/2" X 2 ' long sections of square channel under the frame where the axle is mounted. It will give you a little more height underneath.) And have the new one bolted on, not welded. Easy enough for the shop to bring it up to date.
Here are the Dexter 3,500 Lb. Torflex axle specs
for all the"bolt-on" axles that Casita now uses.
65.5" Hub face
51" outside-to-outside bracket spacing, (where it mounts to the underside of the frame.)
5 Hole on 4.5" bolt pattern for wheel rims.
AP166 Mounting brackets, (for mounting the axle to the frame with bolts instead of welds.)
And also the "start angle" (in degrees,) of your choice: 10up, 10 down, 22.5 or 45 down. What Casita uses now for a low rise or standard axle is 10 degrees up
, and for their high-lift axle, they use a 10 degree down
If you don't want to add the 1 1/2" square channel, then use the 10 up, if you do add the square channel, then get the 10 down axle.