To run an electric coffee make or hot water kettle, you probably need a 2000W inverter. but it depends on the device you are heating. If you have the them, look at the label and see what wattage they pull when heating. That will dictate the size plus a bit of a safety factor. Whether you go 1500 or 2000W, the only differecne in the install is the size of the wires and fuse. I (and others) have installed a 2000W in a TAB 320. I used 2/0 AWG wires and a 225A Class T fuse. If you use welding type cables , they are very flexible and can route easily. If you plan to do it yourself, do a search for inverter install and you can see how I and others have done it.
(I see your from WV...we go to Canaan Valley often)
I agree with @ScottG. Replacing old Rhomar with new you will not see a color change to know if the old has been replaced with the new. Color is a good indicator if you are replacing the old Century with the Rhomar as one is yellow and the other is greenish. As Scott mentioned I would just push in a bit more than your system requires and call it good. Since the color change is not going to be noticeable I would also recommend using a shop vac to suck out the old fluid at the end of the line as you pump in the new. It's the method I used on our 2021 400 and I think it just helps in removing the old and limiting the mixture of old and new glycol.
We replaced the Danby with the Frigidaire 5000Btu unit. It's the same size as the Danby. It has a thermostat, a lower low fan speed and you can select to run on low or be off between compressor operations. The air is a lot colder.
@Greenhil, I doubt you will bbe able to identify old vs new glycol by a change in color, or pH. If you are simply pushing the old glycol out with the new, I would go by the volume of new fluid pumped in. To do this, you would need to determine the approximate total capacity of your system. To be safe, I would probably pump in an additional 10-20% above that volume.
Besides the comfort that the Froli system provides, I believe it also acts as a vent for condensation and moisture that would naturally occur. I wouldn't remove it for this reason. Maybe replace your 3" with a 1". Or remove the lower cushions completely and go with a thicker mattress on the Froli?