Improved exterior wall construction recommendations?

[Real Wrought]

I'm rebuilding my walls entirely.  I want to improve quality in a few ways: add rigidity to the walls, improve attachment integrity for whatever im screwing to the walls (like window frames, etc) add insulation, reduce weight and to eliminate water ingress.  I haven't made all the decisions yet for how I'm going to do this yet and I'm looking for advice.

As this is a functional rebuild I'm replacing the original aluminum siding slats with a thin modern fiberglass exterior.   Any wood framing I build, if I use wood, needs to be more dimensionally stabilized than the OEM pine framing and I would use pocket screws rather than machine-gun staples. 

Question - what works best?  What kind of wood is best for strength to weight or should I weld up an aluminum or thin steel frame for the walls?  Thin steel might not be enough to screw into, I think.  When you did this what mistake can you help me avoid?

[Eyez Open]

Be aware if fiberglass is use one must glass the walls to the wood frame. Fiberglass mechanically attacehed to any frame would be useless...big big difference between the two. One can assume a RV mfg uses glass only for comestic purposes.

There is a process for one could use however, i noticed in my HR the factory blew strands on the aluminum siding then attached foam panels between the alum frame...Using that method would make any facing part of the overall frame shall i say..Below is a video as to blowing chop or strands...it is a close as i could get to the actual process.

https://www.riverpoolsandspas.com/blog/proper-thickness-of-a-fiberglass-pool

Blowing Chop/fiberglass  https://youtu.be/SFjw7daebWE

[Oz]

A long time ago, one of our members, LJ-TJ, bought a Winnebago (a D21, I think), which had fiberglass panel sides.  But, there's more to that in the next reply down.

Take note of the preceding post:
Whatever you choose to strengthen up the framing must be fiberglassed TO the fiberglass panels.  When the Unger family built their motorhomes, they made them with a wood frame reinforced unibody. The wood framing was all fiberglass sprayed and rolled ro the body.  (I did fiberglass layup for transportation for a few years, so I'm a little familiar with the process).

Also, that's not just an aluminum skin, it's adhered to insulation, which is adhered to the interior paneling. 
You will need to fill that gap with insulation.

As for reduction of weight, adding more wood and fiberglass panels will add weight, rather than reduce it.

[Oz]

Read this:

https://www.classicwinnebagos.com/forum/index.php?topic=3754.msg9989#msg9989