Insulation in horse trailer conversion concerns and questions – GreenBuildingAdvisor

My friend just bought a new (aluminum) horse trailer. It has a good size tack room that she would like me to add wall panels to, as well as bunkbeds and a few other fixtures so she can use it as a “weekender” she can sleep in when she goes to horse shows. She had the dealer install insulation, which is just 3/4” EPS  foil faced rigid foam cut in-between aluminum studs/frame and taped onto the studs/frame with Tyvek tape. Nothing filling the space in the channel of the aluminum framing, as you can see in the pics. It’s definitely not the product I would have used to insulate it.

The plan was to install panels fastened to 3/4” cedar furring strips which would be screwed to the aluminum studs/framing of the trailer. I was thinking lauan or 1/4” birch plywood for walls and ceiling with maybe one accent wall of t&g cedar.

My main questions/concerns are:

Will this just invite moisture to build on the back side of those panels, and between the trailer skin and the inside of the EPS foam?  Does the 3/4” air gap created by adding the furring strips help  at all, or make the situation worse? Will the foil face and taped seams prevent any moisture from drying to the inside? The tape over the framing will be penetrated by a lot of screws attaching the furring strips of course.

How best should I insulate all the voids they left (center channel of the metal framing etc)? I was thinking (canned) spray foam or cutting strips of XPS and then everything taped with something better than Tyvek tape.Will this do any good at all, knowing there will still be thermal bridging anyway? I know this insulation job is far from ideal, but I know she doesn’t want to start from scratch so I would like to make the best I can of it for her and prevent mold and moisture issues.

It’s important to know that she realizes it won’t be very well insulated. She’ll mainly be using it in spring and summer months for camping purposes.

There will be no electrical or plumbing penetrations. Just one existing  interior led light. There is a roof vent.There is a screen door. I’m assuming that airing the space out when possible would be a good idea. Maybe adding a supply vent somewhere low to the ground to help with air circulation?

Trailer will be stored outside year round. Pacific Northwest, so not too many extreme temperatures, but lots of rain. 

The floor will have no insulation. Just LVP wide plank flooring on existing plywood floor.

My main concern is that the work I do for her doesn’t create an unhealthy environment by trapping moisture and creating mold. She’s not expecting a super well insulated space, but wants it to be practical and look nice.