Peltier technology dehumidifier. Does it work...yes. Does it work as good as a compresssor type dehumidifier...no. Lots of trade offs in the comparison. Countering high temps and humidity in getting an RV cool has not been a one solution fix, from my experience. The Eva Dry 2200 pulls about a liter over a couple days give or take on how high the humidity is. It doesn't weigh a lot, draws very little current, makes little noise, stores easy and doesn't release a bunch of additional heat into the RV that you're trying to cool. My TT came with a 13.5 KBtu Colman-Mach( optimized, with special thanks to Herk on the forum) As to your ? of electronic dehumidifier or 2nd AC. Long green difference...<$75 to ? and probably some extra power needed to run it.
Mine is OK tolerable and the AC does cycle, considering, digital t-stat, 3 air circulating fans, foam heat blocks added to ceiling vents X3 and the skylight in the bath. Good camping
You want to do a SEARCH on ACs, essentially you are going to seal the hot side from the cold side and seal up the duct work gaps with aluminum tape, maybe self adhesive aluminum duct wrap (R3) is what I used. Others have had results with reflectix. It will, combined, all have a positive effect