Adding Air conditioner to 2003 27/20

[Tee-roy]

My 2002 27/20 SL didn't come with A/C, I want to add it.
I'll be camping in Michigan this Summer.

I'm looking at two options:
A portable household A/C unit, around 15000 btu , I could use it to cool an upstairs room in my house when I'm not camping. Anyone have any luck using one?
Adding a roof-top RV A/c unit around 15000 btu. I've found threads covering replacing an existing unit but not adding A/C to a camper that didn't come with it.

All ideas are welcome and appreciated!