Just wanted to post this as a heads-up for other 312 owners. Ours is a '14 model. Overall it's been a great trailer - however there have been two issues that have been nagging almost from the get-go.
#1 is the sink. It's only held in place with 3 small hangers that are screwed into the underside of the counter. With the heavy sink covers and lots of bouncing down the road and load from doing dishes we've had a hard time keeping the sink tight to the counter. Usually I first notice that the sink covers are no longer sitting flush.
I have tried adding more screws, more hanger straps, and even some plumbers hanger under the entire sink to no avail. Here is the latest fix - I made 4 legs out of PVC that when all joints are tight just wedge up to the sink. I can then loosen a joint or two to extend the leg which tights up against the sink:
#2 is the bathroom sliding door. We love how it makes us feel like we have a master bathroom, but we have had a hard time keeping the door secured to the wall. There is no inner wall support behind the lower slider rail so the screws holding the slider to the wall are only biting into the paneling. The screws into the door have also loosened up and stripped out with repeated tightening over time.
The door was barely hanging on - so it was either try to improve it or remove it and settle for a curtain in its place. I choose the former - my fix ain't pretty but I think it will work.
I mounted (clear-coated for rust-prevention) strap steel to the other side of both the wall and door and replaced the wood screws with through-bolted machine screws:
If you have a 312 I'd recommend inspecting these two items to see if you are having the same issues.