[BiggarView]

We're having same issue on our 2020 3813, I determined the leak was coming from the shower drain which has come loose from the pipe that goes to the gray tank though water flow (98% is going down the drain) is not a lot but it is a sign of future problems if not addressed.. Our RV dealer said we will have to cut into the coroplast and then cut through the main floor in the "crawl space" that as you say is inaccessible through the kitchen or the front door or the basement. Our plan is to open the coroplast to inspect for the best route. Then cut a rectangular "trap door" if you will (about 18-20" wide and 12-15" across) in the crawl space floor near the shower drain pipe to provide the access from under the RV. Hopefully we do not have any frame or other items blocking access) Once addressed I will screw two strips of wood longer than the length of the rectangle cutout so that it will rest on the floor when replaced. It can be screwed from under the floor to the strips to hold it there. then the coroplast can be resealed. The tricky part will be making sure the pex tubing for the shower is not in the way of the cuts as it lays on the crawl floor but it appears, from inside the RV at least, there is room to make the cut safely just have to use extra care.

For now I silicon caulked the shower drain to stop the shower water from leaking around the outside of the drain pipe, which is working as "band-aid fix" until the repair is made I have a shallow clear storage bin finagled under the shower elbow pipe with some fabric wrapped around it to act as a wick which then will draw any water into the bin which I put a towel in to absorb the water and allow it to evaporate. So far no issues. Not perfect or preferred but it works for now.

Lack of access, to this item is IMHO, a design flaw in the 3813/12 and the 3810/11 models. It was also a compromise to provide the extra bathroom headroom that we like about the plan but which could have be addressed in the design phase.