It depends up to you really...
Rafa's guess is that his case would be just one of the many cases brought in today, the team's got the badges saying they're supposed to be there and supposed to be delivering props and they are expected there. So he guessed that after the badges check out, security won't really be very suspicous anymore. IF they decide to check the cases, there's enough metal in all the cases there to make MAD scanners go off anyway, if they pick out some cases at random and pop them open to check the contents, pretty much all of them will contain exactly what they're supposed to contain. If they pick out Rafa's case it will contain some random useless crap and his lunch kit. There's a hidden compartment (see the False bottomed attache's case in Arsenal, only with -6 to their perception instead of -2).
But well, to be honest, from the description of our arrival, security didn't seem -that- tight.
If Rafa spotted such a heavy security check, I guess he would have tried to find another way, if that seemed too risky to pull of, he would just leave his gun outside... it not like he's defenseless without it. For him, his rifle's just an easier way to NOT kill compared to being unarmed.