Almost ready to dive in

Welcome teacherman,

It sounds like the previous owner (P.O.) tried to repair the trailer by gutting it from the inside first. This method presents several difficulties, resulting in dilemmas such as what you find yourself in. It seems counter intuitive, but due to how these trailers were originally constructed, and how the structural integrity is integral to this method of construction, it is best to repair these trailers in the exact opposite order in which they were originally built, from the outside in. Once you get going in this order, it is pretty easy to figure out how approach the repairs.

There are many, many threads here demonstrating this method. Take some time and peruse the forum to see how others have done this.

Also, Larry (mobiltec) has a great website loaded with videos of nearly every aspect of trailer repair: www.cannedhamtrailers.com/

One more thing, we like pictures here.

If the other rear corner is still there pull the outside skins and you will see how it was built. Then match it on the other side.

Thanks for the input! The right rear is the side that she removed. The left rear inside the bathroom is intact. It looks to have water damage too. A couple of questions:
1. If the water damage on the wood is just darkened and stained but not necessarily brittle or soft does it need to be replaced?
2. When building the rounded corner with plywood strips should this be built and layered on the frame or assembled separately and then installed as on piece? I'm concerned about getting the curve right.

I'm sure I will have many more questions as I progress.
Oh wait, one more! Should I pressure wash the outside before progressing with the frame or should I wait until I think the frame is done and all sealed up? I'm thinking I want to get some of the major dirt, grime and remaining paint off now when I know that any water inside won't be hidden and cause future problems.