Split the coach in half (up/down not left/right) at the floor, chassis and house. Ford is your go to for the chassis and a laundry list of manufacturers for the appliances (A/Cs, TVs, microwave, water heater,,,). Regarding the structure, plumbing, wiring, roof and such you need to think more along the line of the brick and mortar home. There might be design drawings, material listings and such but you'll find little regarding how the builder would repair/replace the roof, flooring or shower enclosure for example.
Fortunately there are owners who document their efforts and post to Youtube, forums and personal blogs regarding how they did the work. Don't fixate on Newmar and think concept or general application regarding repairs. Newmar may have aluminum cross members rather than wood in the roof but it's still a synthetic membrane glued to light ply and cross members when you start peeling the layers back.
Work directly with Newmar for the design drawings and such but don't get your hopes up to high. 20 years is a long time to keep documents, even electronically. For the chassis eBay might be your best source for the chassis repair shop manual.