I concur with all of the advice you've been given - especially to do understand RV Systems, know what is quality work, and use quality materials whether it's a restoration or an update. TAKE A COURSE or two before you start trying to make cabinets or upholster furniture the first time. Adult ed. courses are common in local high schools and community colleges. Many specialty stores offer courses to help move their fancy tools too.
I'm not saying that you shouldn't make curtains out of pretty sheets if that's what you can afford - especially if the old ones are missing and you want to go camping next week - but that's easy to replace and doesn't damage the structure or surfaces of the interior. No one will pay big dollars if you want to sell a trailer that's been "decorated" with stick down tiles, peeling latex paint and a 10 year old futon couch that cost $99 new.
I've walked through a "completely upgraded trailer" where someone put a 20 gallon home water heater in - in place of a twin bed, complete with visible plumbing, and replaced the toilet with a home model AND used a residential refrigerator. It all coordinated nicely with the mouse poo smell.
My personal favorite was here on the forums. Two by four construction and a claw foot bathtub! Jeez, can you say "break the frame!"
I would actually hire a designer to help me put a concept together - I tend to have semi-decent taste, but a professional can take my basic ideas and polish them with a few throw pillows or a different wall clock or something as simple as changing the salt and pepper shakers and lamp shades.
Make a plan and follow through... with reasonable revisions as you make discoveries.
Most of all see you down the road. Paula
Today is a gift, that's why they call it the present.