Uh...I don't think a 15 ft trailer is going to be a decades long project.
Memories can also be made with hammers in hand. I have a few of those, my Dad was a very resourceful guy.
For cost projections--My final remodeling costs on a 22' ft. gut and rebuild were at almost exactly $4K. The trailer cost was $700. That cost included new windows, replacement of all electrical and mechanical systems, building materials, and new mattresses and cushions. I saved some fixtures that were still usable and had some small bits of building materials on hand.
The great thing about the total restoration is that you can lay out the predominate aspects to fit your own personal use. Also, upgrading insulation is not trivial. I enjoy the benefits of that every day.
Folks with new trailers are envious of my counter top space, too. I probably have at least twice what a similar sized trailer comes with.