When I started my trailer re-do, Belegedhel and others gave me similar good advice. I now have a beautiful, dry, updated, safe and comfy Overlander, just like I want it.
A few comments:
These trailers almost universally have rear-end damage due to the bumper area design that channels water into the subfloor. The only way to know the extent, and to assess the status of the rest of your frame/floor, is to remove the belly pan. To me, this is essential to mapping out any sort of plan.
75% of my frame/floor was in perfect shape, but with the rear-end repairs plus replacing belly pan plus adding a grey water system, I would have been better off lifting the shell. I did all the work myself, outside, on my back, and the shell-off method would have saved me much time and effort. It did, however, all work out fine.
The full Monty threads http://http://www.airforums.com/forums/f44/links-to-the-major-renovations-35399.html
are a must to review for any newbie.
We all appreciate the process re-doers go through, and there are many experienced folks much wiser than I (Toastie and Belegedhel, e.g.) who can help with almost any bump in the road, so I second the start-a-thread suggestion.