28 footer is a single A/C enough for hot summers?

My single 15,000 BTU A/C does great in my 38' overall quad slide TT. However, it's better insulated than most TTs and is white.

My 41' weekend warrior also had a single unit. It could maintain the inside just fine, but it was slow to cool an already hot trailer. Since it only had one slide-out, it had less air-leaks, but that ramp door can be a huge heat sink in the sun.

I suspect even that trailer is pre-wired at least.