DrJJL here regarding the 1989. IMHO no good design came out of the 80’s (but a beautiful gal was born in ‘88 but I’m biased on that!).
We have a 1985, we are second owner and we are a software engineer and a nuclear medicine doctor: no construction experience whatsoever.
We started the do-over last spring and stopped in the fall, now re-starting.
With the 80’s models:
There was a cardboard wall for a shower wall
All the fake oak and antique white contact paper were self-peeling
The T molding was breaking
Most of the ABS plastic parts were cracking or were going to crack
The fresh water tank sprung a leak
The AC bit the dust
The carpet and accordion doors were NASTY smelling
The twin bunks were uncomfortable and too small for 66” adults
The gaucho was both uncomfortable to sit on and to sleep on
My advise at this point:
If you have the time, it mostly can be done DIY.
Save your parts. Label them.
Upon removal check you floors. They are integral to the structure. If major repairs on subflooring is beyond you then contract this out.
Replace tanks and plumbing as needed; go with PEX and diy that part.
Of course test electrical
Try to save end-caps; repair-in-place (don’t remove if they are salvageable) (this is the only original ABS I saved.)
Buy a fiberglass tub base
Try to keep the U channel that holds the bulkheads in place until you come up with your space plan; that way they won’t get bent or lost.
Plan to keep or replace appliances and tanks in their original position replace water heater if necessary; service furnace. Keep original range: don’t get rid of it at the onset; store in a shed or the garage.
We went with lift-up rear bed to replace twins, sold gaucho and built in a conversation sectional with rounded corner sections; but then we didn’t need extra sleeping surfaces up front.
We replaced all bulkheads with Baltic birch plywood with laminate faces (lumber supplier did the lamination and we used original panels as template)
We only had to move one U channel to move the “cabinet for my long formal gowns” up front to make a cupboard)
We replaced oak doors with laminated doors from Lindsay Doors of So Cal. Sleeker look. Antique White.
We stick built vanity and galley frames then using original aluminum as face frames
Replacing yellowed tambour in end-caps with spray-painted cuts of bamboo rug to match rose gold trim.
Using click wood-look flooring.
Replacing galley countertop with solid surface and composite sink (hence needing the stronger frame)
Replacing 80’s Magic Chef with 70’s stainless Magic Chef range (keeping the original for parts)
Got rid of spice cabinet behind the stove
Put in a slide-out where front accordion door was next to the vent stack
Just my thoughts
Talk about use and design to fit your needs: it’s YOUR trailer you can do what you want.