Flight from Trat to Bangkok (BKK) with only 50 min connection, possible?

I will be traveling around Thailand in January.  My last stop is Koh Chang.  I want to know how the Bangkok airport works.  Here's what will be happening:

My flight back to the states leaves from BKK at 11:50am.  I want to take a flight in order to get back to Bangkok from Trat on Bangkok Air earlier that morning which is possible.  However, the flight from Trat will arrive at 11:00am.  This gives me a 50 minute layover but my next flight at 11:50am is on a separate itinerary.  I can check in for my main itinerary via the internet and will only have carry on bags, so that won't be an issue.  

My only concern is if there is some policy where I have to go back through security.  I don't think I should as I will already be in the airport with my luggage, but I don't know for sure.  I would think I would only go through customs in my gateway city when I arrive back in the states, right?  Thanks for the help!

Bangkok (Thailand)   Trat (Thailand)   Koh Chang (Thailand)