I will warn you about this. Your camper will not be set up to suport the weight of a roof top unit. It can be added but it does require a lot of work.
Here is a link to that thread.
Somebody else also told me to check into some of the A/C they are using on pop ups and such. The A/C unit doesn't go on the roof it would install in the side. I have a friend with such a camper but have not camped with them yet this year so I have not had a chance to look at it.
It would require an outside vent of some sort. I'm hoping that I could vent through the floor like the Reefers do and then just add a outside access door that would appear original. On our 59 we have a side access door. We also have a spare tire carrier. That particular area is under the bed and I might be able to install the unit and access door and have it hidden by the spare.
I want to look at one and hear how loud they are since I would basicly be sleeping right above it. Then make my decision as to what one will be the better option.
Right now I have a awfull looking window unit through the front window that the PO's PO installed. It will stay till I can locate a window.
Please update us when you make a choice. I would like to hear your solution. I have already put that change as a next year project. I'll be replacing floors this year.