I would recomment a pair of Fantastic fans. You can set them to blow in or out. They move about 250 CFM at 12 volts, you can run them without hookups if you need to.
For the A/C then the largest one possible.
For the heater, I would use a portable one. This way if you are limited to a 30 amp circuit, but might be plugged into a 15 amp receptical, you can always find another circuit for the heater if you really needed it, but if it is wired into the A/C unit, you could not use that and still stay below the 15 amp limit, without shutting off everything else in the RV.
Besides a A/C system the heating element option is normally well over $100, they are not worth it, a good portable heater only costs about $19.
If you have humdity problems, consider a 65 pint per day $250 dehumidifier from Home Depot. Rated to remove 1.85 pints of water per KW of energy used, it will work on much less power than the A/C unit, and effectively dry out the air.
Fred.
