Agree with what others have said for your unit. If the box is already hot, say 95+, your one AC isn't going to get it cool. If you want to keep it cool, you have to stay ahead of the curve. Start you AC before you need it on the morning if it has cooled off during the night.
Also as was said, the two hose portables are the way to go if you are going to use a portable. The single hose coolers are just a spot cooler.
Use shade if you can. Pull in any slides you are not using. Slides are more roof under the sun and more volume to cool.
I crack ceiling vents about an inch. The hottest air is in the ceiling, I want to give it a chance to escape. The jury is out on this as it can be counter productive, same as single hose AC. I've tried it when trying to catch up with the heat curve and it seemed to help. Once the rig gets cool, close them.