We bought our Catalina 20RD TT about 3 months ago. It's our first TT and I haven't been able to resist doing various upgrades/mods.
The first one was to install a recessed electric heater in the ceiling. This will let us keep a minimal amount of heat in the trailer over the winter (about 45F or so). Also, this heater is WAY quieter than the Suburban furnace which sounds like you are parked next to an airport.
It's a 1000W axial fan type made by Q-Mark. I researched every one available on the market and chose this one because it allows a closer (12") clearance to sidewalls and has an extension frame (available in 1" or 2"). The ceiling cavity is only 4 3/4" deep so the frame allowed my to have about a 2" layer of insulation above it.
After cutting a hole in the ceiling, I was able to fish the wires over to the fridge (after pulling it out) and down to the electrical panel. I installed a low voltage heating relay and transformer behind the elec. panel and ran LV wiring up to the thermostat in the cavity behind the bathtub. I wired it to the panel and installed a new 1P-15A breaker. Not worried about the increased electrical load as the A/C unit won't be turned on at the same time as the heater.
I'm really happy with the end result and it looks like it might have been installed by the TT manufacturer. Still patting myself on the back.
While I was pulling wiring into the walls and ceiling, I also installed a coax cable for the TV from the rear of the trailer to the opposite side near the door and at the end of the kitchen cabinet. Along with an articulating arm TV bracket, we'll now be able to watch TV in bed and from the dinette. We bought a 19" LDC TV with built-in DVD player which solved where to put the DVD player.
Now with a warm trailer in the winter, I'll be able to watch TV while doing the rest of our planned mods like adding a couple of cabinet doors, cabinet shelving, fixing the wobbly (factory standard) table, counter extension and towel rods.