I just found an almost identical crack on the 1994 Casita SD that we bought recently. I had to replace the bearings, bearing races and brakes
(whole brake back plates). While I was at it I decided to wire brush the frame -- and treat with rust converter. After wire brushing the dirt and surface rust I found a single crack (just like the left hand crack in the photo). If I had not done the wire brush prep I never would have seen the crack. I'll get it welded ASAP prior to any trips. I think I'll wire brush the axle
mounts and inspect them on a regular basis! I was going to paint
the frame with rustolium, but I think I'll just leave it with the primer finish created by the rust converter since it dries clear and allows a visual inspection for cracks. The paint
might cover up hairline cracks like I just found.