Very common to have the freeze sensor fall away from the evaporator and the compressor does not cycle as designed. Remove all interior trim and check the sensor. Or did the service person show you it was in the right spot? And check his work on those ducts too... it sounds fishy but odd things do happen.
While in the check the plenum divider. This separates the air-in from the air-out and they are often poorly installed allowing air to re-circulate in the unit instead of cooling the RV. Get some tape and seal it up.
Humidity is bad but 90 is just the start of getting hot. Shade always helps.