With RV toilet paper or Scott's 1 ply toilet paper, the paper should dissolve fairly easily in the tank if there's enough water in there.
I'm not sure if the 2012 models had one, but it might have a sewer tank flush. If it did, it would be just above and to the right of the left fender, left of the water connections. If you have it, that's the best way to clean out the blank tank. Just hook up a garden hose (not your drinking water hose) up to the sewer flush inlet, open the blank tank valve, and start the water. This does a pretty good, though not perfect, job of cleaning out the tank.
Another method that I have used is to put water softener into the blank tank. This helps to clean the sides of the tank. Since you're having an odor issue, I would recommend that you put half a box of water softener in addition to a dissolving deodorizer/sanitizer into the black tank and then fill it up about half way with fresh water. Then go drive around in a big empty parking lot or other big space and make lots of turns so that the water sloshes around really well. Then let it sit overnight.
If you still have an odor, you may need to get a toilet wand that hooks up to a water hose. You have to stick this down the toilet and work it back and forth with water running to clean out the tank. I wouldn't recommend this unless everything else fails because it can be a really nasty job.