Terry,
You'll find out soon enough that we did not buy a Challenger, but I've thought about and solved some of the problems you're facing. On the wood house sides, I think that veneering is a viable solution. They're large thick hunks of wood with transverse bronze drifts to keep them from splitting. To replace them is a normal, but arduous and expensive repair. Besides deterioration at the corners and behind the coamings, these things loose thickness over time to refinishing and to weathering. I think that you could remove the ports and trim, use a power plane and make the surface planar, laminate a bit of 'glass onto the clean surface, laminate a new exterior veneer, varnish and reinstall the ports.
I'd worry about the joints and transitions and decide whether I was effectively making a fiberglass house or repairing the wood components of a wood house. It's an important distinction and has to do with whether subsequent repairs are possible or easy. My gut reaction is to repair the wood components but that leaves those forward corners as vulnerable as ever.
The idea behind overlaying with glass is to ensure that the new veneer is unaffected by the movement and cracking of the original house sides. The important negative is that the assembly is grossly assymetric, but so is the effect of heat and damp. Normally, one wants an assembly to be symmetrical (equal lamina on each side) so that it's tendency to warp is reduced.
One might estimate the loss of thickness of the original wood over the last 45 years. On our 1970 Northeast 38, Quetzal, the coamings are now about 13/16" thick but started out at an inch, and the plywood companionway boards were sanded through to the next veneer. On our previous boat, a '72 Morgan, the unfinished companionway boards started out at a heavy 3/4" but were taken out of service at a light and severely cupped 5/8". On one Challenger I looked at, I estimated the loss at around 3/16" and it was quite severe at some of the drifts.
Thus, I'd suggest a veneer of 1/4" solid wood which would give you and your successors lots more time. !/4" is about as thin as you dare run through a planer, having resawn a plank. You can buy boring quarter sliced mahogany veneer 1/8" thick, too, but it would look like an European piece of furniture.
I did my replacement companionway slides for Quetzal with 3/8" Makore inside and 3/8" Teak outside with a fiberglass layup in between and the whole things are breadboarded in Teak. They Look like the originals but there's lots of wood to sand. (I can share or post photos, but my computer skills are not equal to the latter.)