Glocks; sand-desert conditions, M9/M9a1....
I've heard & read posts from a few SW Asia combat veterans/PMCs that Glocks have major problems with sand-desert conditions. I'm not quite sure a Glock pistol would be ideal for the hot weather or sandy conditions.
The elite SAS(Special Air Service) of Great Britian selected the SIG-Sauer models(P226R/P228R/P220R) over Glocks saying they held up better in T&Es.
If it were me, I'd look at a used M9 or LE trade-in Beretta 9x19mm/.40S&W, model 92/96FS. Beretta service size pistols have been around since 1985 or so and many US police agencies have started to turn them in or adopt newer models(M&Ps, HK, Glock, etc).
The open slide design won't trap sand or grit but it may get a lot hotter with +P/+P+ rounds. The older 92F/92FS pistols are easy to clean & service too with a good CLP like Gunzilla or LPX.
I wouldn't go with any caliber smaller than a 9x19(9mmNATO) for a "beater" gun. You'd want a firearm that could protect you in a critical incident & function properly. I don't know how you'd defend or explain a old, worn out firearm in a small caliber in open court.
You could find a used Taurus PT92 or .40S&W(PT100) too.
I do all my own stunts.