I am installing the original skins. I am still giving some thought as to whether or not to overlay them with something else in specific key areas. There are wood products that are very thin that could be used to overlay the aluminum skin so that you would have the best of both worlds - the strength of the aluminum and beauty of the wood - and still not add too much weight.
Check out the following sites for sources of all sorts of flexible wood veneer products.
Oakwood Veneer Company :: Wood Veneer Maple Oak Wood Veneers Exotic Burl Manufacturer Supplier Custom Wood
TAPE-EASE: WOOD VENEER EDGEBANDING & WOOD SHEET VENEER, PVC, CURVED PLYWOOD & Much More
Unfortunately I do not have any direct experience with any of the above companies or their products. I do know that it is possible to buy 1/8" thick plywood here in Portland in 4'x8' sheets for pretty reasonable prices the last time that I checked. Many of the products listed on the sites above are specifically designed for overlaying. There are all types of woods. I would actually be interested to hear from anyone on the forums that have experiences with any of the above companies or their products.
My general thinking is that there will be lots of places in my trailer that the exact nature of the skin will not matter all that much. Who cares what is behind the kitchen cabinets or the shower surround for example? Why not concentrate on adding the eye candy in the places where it would be most visible. Maybe even start in one place and see how it works. Add more later as the concept proves out and as the budget permits.