Montana loves to use "DS" and "ODS" meaning "Door Side" or "Off Door Side" to them. Everybody else in the world who sees "DS" thinks "Driver's Side". But we digress from the OP's list of issues.
Here are my random comments/observations/opinions of some of the OP's issues:
" water came in behind the fridge. " Yup this a long standing problem with refer vents in the slide and horizontal rain. A piece of 90 degree aluminum channel siliconed on the bottom of the vent solves the problem. If the Search function was working you could find the numerous postings on how to fix this (with pictures).
" Toilet seat is mounted slightly( about 1/2") off centre." Strange as the "plastic nut" on the bottom side should center the bolts in the holes.
"Outside door has no latch on side of trailer to keep open." That is the new design using "friction hinges". They all come with them now. If you are in a windy area you may need to add a door latch available at CW or RV stores
"A/C in L/R drips water thru vent onto the floor" Another known problem that has been discussed. Could be the seal or the drip line is goofed up. I know there was something recent but but I can't find it. Maybe another owner will remember.
The fit and finish issues are not unique and should be addressed by your dealer. Montana seems to use them as the quality control staff. It isn't right, but it is the way the game is played today