RUBBER ROOF ?

Yep, my rubber roof was always loose in lots a spots, especially around the edges, but it never hurt anything. The only problem w/ a rubber roof, is worry'n about it.
Just carry a roll of eternabond just in case. I carried one for 12 yrs, never needed it.

What do you mean by "looser along the outer edges"? Air under the rubber? If you walk over it (yes, walk, just put some plywood strips or do it on all four and try stepping where rafters are), you will find plenty of air pockets on it. Most of them have been there since day one. Some settling of wooden structure is possible though. I doubt that a trailer that costs 30K has much less air pockets on the rubber EPDM roof than the one that costs 12K. Same EPDM, same 3/8" particle board underneath.

The danger is when the rubber wears through on the edges or along other stress lines, ex. along the trim or around the roof superstructures. Then it may separate and the highway wind will rip the flap off, leaving the damage few feet wide. Then you will have to do rubber repair on this area.

Yes, it's normal for them to be loose at the edges but it's mostly because they didn't care about how they were installing it.
Still, mines been that way since new and is still in perfect shape.