I'm sure those books are wonderful and have a ton of lessons learned. My advice to your specific questions:
- I like untucked wheel wells. You make a more narrow trailer for tight trails and have a built in step for the roof rack, or table to sitting things.
- Water heater, many like the Joolka or similar products
- Camping with the dogs, put an awning room on the side of the trailer for the dogs...if they will tear through canvas or a screen this wouldn't be a good idea
- Exterior, whatever offers maximum protection from rain
Hope that helps.