If you're truly gutting it, then now is the time to update the systems.
Replace a thirty year old univolt? Ya think?
I gutted my '73 Sovereign
and scrapped it all. Took the interior to the local landfill and deposited over 1400 lbs of Beatrice interior, not including the fridge.
I'm in no rush to finish the refurb, so I'm replacing everything, as time and finances allow.
Some other things to consider include:
1. Replacing the water heater with a tankless unit.
2. Replacing the roof AC with a more efficient unit that also has a heat pump.
(and adding a wall mount radiant unit) This allows you to lose the 30 year old furnace entirely.
3. Lose the oven (unless you plan on cooking that Christmas turkey in it.) in favor of a micro/convection unit.
4. If you're not towing it, then an electric fridge is more economical to run.
If you're going to spend any real time inside the trailer, you might want to consider altering the floorplan. I'm eliminating as many of the vertical divider walls and as much upper cabinetry as possible. This will open up the space significantly and make it seem larger.