First, welcome to our forums. You will find lots of help here. Now to answer your questions as best I can..
1. What temp is your AC set to? Is it set to AC, Heat or fan? I can't help much on this one.
2. Typically the filters are in the large vent openings. Do you have 1 or 2 AC's? There is typically 1 filter per AC. These can be washed out and reused.
3. Beep beep beep is likely the CO more Igor (usually low to floor) or smoke alarm. Check their batteries. If your coach battery is dying, you have a drain. When not in use refill the battery disconnect switch. If yours is not equipped with one, they are cheap and very easy to install. A trailer will always have a parasitic drawing the battery is not disconnected and will go dead in a couple of days. If you are dry camping, the battery will drain quickly if you don't conserve power, have a generator or solar power charger. Several threads on how to conserve power when dry camping. Try a search if that is your issue.
4 what kind of smell? More info needed here.
2014 Crew Cab Chevy Silverado 3500 4wd Duramax/Allison
2014 Sabre 34REQS-6