There should be a panel in your basement storage area that is removable. Once it's out of the way, you should be able to visualize the top of your holding tank, the bottom of the shower and all the associated plumbing.
I believe that the showers in all Keystone fifth wheels since about 2014 have eliminated the "P" trap and have gone to a Hepv0 waterless trap. There is some information on this type of trap here:
http://www.drainmaster.com/main/2011...to-the-rescue/
As for the dripping water, possibly a loose/leaking connection at the vent, a loose connection on the Hepv0 trap or the shower may have "leaked" between the floor pan and the side wall ??? Only a good visual inspection will reveal the source.
Good Luck