Nope, no charge top-off needed -- the unit is sealed and should never need a re-charge. As to discharge air temp, using an infrared thermometer, below 100F, my roof vents normally put out air in the high 30's/low 40's.
You don't tell us what year you Adventurer is, but there are two likely problems.
1 - the air duct is leaking behind the rear cap. You can normally discover this problem by lying on the ground under the right rear and reaching your hand upward behind the cap by the duct, and/or reaching up on top of the horzontal duct where it makes the turn to go upward. Mine was leaking badly at that turn, on top. If your duct is leaking higher up, you might determine that by running the ac unit on a hot day and feeling the outside of the rear cap from bottom to top of the right side. A cool spot would likely indicate a duct leak at that point. If you cannot reach the leaking spot from the bottom to apply tape, the rear cap has to be removed to make the repair.
2 - A bad start capacitor is preventing one compressor from starting. Start capacitors can be serviced w/o removing the ac unit from the coach. When running the coach on 30a or generator, you can tell if both compressors are running by watching the amp meter inside. When the unit starts, one compressor starts up and pulls apx 17a. Apx 2 min later, the second compressor kicks in, and both together pull apx 23a.
With the temps you report, I suspect your problem is separated ducts. I believe even just one compressor would do better than your temps at ambient temp 70-75.
To find a qualified service location near you, check the RVP website at
http://www.rvcomfort.com/rvp/service/need_repairs.php and look for the letters "uf" in the "Services Provided" area of a service location listing. Unless your Adventurer is still under warranty, Winnebago dealers are not necessarily the best place to have the ac/heat pump unit serviced.