Linda - The 'Kraft' side of the insulation is the vapor barrier. It's normally placed such that it's FACING the warm side of the house. In other words, if you're in the house and looking 'down', you should see the Kraft; not the insulation. If anyone else has an explanation as to why the Kraft side would be placed to the 'cold' side, I'm listening.
Jane - I wouldn't install a vapor barrier on the underside of the home because, as Linda states, you will trap moisture. Even with the Kraft paper facing up, moisture will 'migrate' around the paper, thus, allowing the floor to somewhat breathe. It's quite possible that by removing the 'old insulation', you removed enough of the Kraft-sided insulation and, now, moisture is 'settling in' your flooring.
A contractor may recommend one of a number of options for which you are to ask him to explain: 1) Lay down some 6 mil poly plastic (and put 'bricks' around the perimeter) all underneath the trailer. 2) Lay down the poly as in #1 AND 'seal up' the area around the trailer. 3) Remove/move ANYTHING that is obstructing the movement of air under the trailer so it can be 'aired out' and 'kept dry'. What you also might try and do is run a dehumidifier when you have the doors and windows shut (and the A/C on.) At the same time, talk to some pros about redoing the insulation job with Kraft-sided insulation. See what they say about putting the Kraft up facing the floor (or down facing the ground.) You can still do the job yourself but do talk to 2 or 3 so you can get a bit 'educated' on this situation.
As an aside, we have a 30' x 15' addition with a poured crawlspace that's 3' high. It's unheated/uncooled - It's basically outside (but completely enclosed with cement block, and vented.) Anyways, above this 'space' is 1/2 of the kitchen and a family room. With this 'setup', we DON'T have wood floors in the family room or in the kitchen. The FR is carpeted and the kitchen is vinyl sheeting. 2 years ago, I re-insulated for the same reason you described and installed the Kraft-side up. (It faces the 'heated space'.) The insulation is 'laying' on a woven mesh of nylon string that I ran all around and along the joists under there. I simply nailed in small nails and ran the string from nail-to-nail so that the insulation now 'lays' on the mesh of string I installed. It's nice and warm in the winter and I have no problems with moisture or rot. I do go 'in there' once per year.
Others may have more to say. If you have more ?'s, e-mail me directly or post up. My best to ya and hope this helps.
PS: If you're able to 'reduce' the humidity, and the floor doesn't return to its normal state, you may have to replace the flooring. If you have a laminated flooring, the damage may already be done and you'll HAVE to replace the floor. Sorry, you didn't say what you had for flooring so I can't say if it will 'return to normal' at some point.
PPS: There is a 'Technical Note' to Fred's Radiant Floor Barrier System. It's important to read it because it speaks, directly, about trapping vapor! TECHNICAL NOTE: When an interior barrier is used, all seams should be taped to avoid possible moisture migration. When an exterior barrier is used, it should be perforated unless a vapor retarder is used on the interior side, otherwise it may trap moisture. Application techniques will vary depending on the climate in which radiant barriers are used.