Replace HVAC or add second unit

[barnetts]

Greetings fellow Airstream owners. This is my first time posting a question but I have been following and gained much knowledge from here! So thank you all for that! My wife owns and I work on a 71 Sovereign (Betsy Ross). We are looking at doing some summer camping this year and we live in Alabama! It gets frog boiling hot in the ponds down here. So my question is this:
The AC unit appears to be original but still cools (at least the back half) and with fans we can feel it up front. Would I be better served by adding a second smaller unit up front or replacing the original with a newer and most likely more efficient unit?
Thank you in advance for any response!