there would have to be a reason why that cannot keep a 24' trailer cool... We had several RV's over the 30' with 1 13.5 AC for years and it worked.. Not the best at all times , but manageable.. Each of those spent 2 weeks in July/August on the beach at Myrtle Beach with no shade..
As far as a second ac goes , Your trailer would have to be wired for 50 amp in order to do this. UNLESS-- you create a separate plug for that second AC to plug directly into the pedestal ..
I would have that AC looked at before spending a ton of money adding AC's and wire.....