NOTHERMARK: Great ideas! I'll address them one at a time.
I decided to look at the barb fitting vs the shark bite, neither of which I'd ever heard of before and I agree, I think the barb fitting would be the better of the two. Glad you pointed out the difference so when I go to HD or Lowes I'll know what I'm looking for. I already have 2 brand new metal clamps and I have a couple plastic ones as well so I think I have the clamp issue covered.
10-4 on the vinyl fail. The previous owner made a few "additions" to this place that were great ideas but apparently he wasn't all that smart about how to do it. For example he added some nice under cabinet lighting over the kitchen sink, an outside light over the dump valves for the gray and black tanks (for night dumping), etc. There's no telling what this guy did to this thing but whatever it is, he clearly did the work himself and he was no professional. What he did LOOKS nice but, as we can see, it appears he made some pretty significant mistakes.
When I tightened the current clamp screw on the back of the toilet, I did borrow a socket wrench and tightened it down best I could given how close to the wall it is. Yes, it was the ratcheting type and it doesn't leak nearly as much as it used to. I need to get me some of those....... I'll add it to my ever lengthening list.
I was up on the roof about 2 weeks ago and I caulked the crap out of it. I made it kinda thick and smoothed it like I was frosting a cake for aesthetics purposes. I did look at the caulked areas around the tub skylight, the vent pipe, the roof antenna, etc.... they all looked pretty good except the roof antenna thing but I took care of that. Again, I'm an over-kill specialist. I don't like to do things twice.
Anyway, the pipe seemed to be pretty well caulked and sealed but once the weather clears up and warms up again I'll go up and check it again. I had planned to check the whole thing in the coming weeks again anyway.
I now question if the drain lines are your problem. You could either have a pressure leak or roof leak. The roof leak could be the sealing around the vent pipe that goes through the roof. If you are on "city water" and have a pump you could try filling the tank and cutting off the city water. Listen for the pump running when it should not be. A leak will cause a pressure drop and pump cycle. Another test is to turn off the pump and see if the leak continues. Harder to judge as you do not have a good idea about how fast the leak occurs.
This is where it's going to get a bit "sticky". I AM on city water. I have never had fresh water in the tank here cause I just bought it (first time RV owner) and it was parked and hooked up immediately so I could live in it. I don't know how that whole fill the tank idea works but I have my assumptions....
If I were to fill the tank and run the pump, I don't know if I could hear it. I am severely hearing impaired and wear bilateral hearing aids. Where I am parked (it was an assigned spot and I don't have a vehicle to move it with) I am about 100 feet from a 6 lane highway. The loudest sound I hear is constant traffic. Even with my hearing aids set to muffle background noises (which doesn't work very well) I still hear the traffic more than anything else. I even have to turn the TV up loud in order to hear over it. At least I THINK I turn the TV up loud....I really have no way of knowing because I have no clue what normal sound is like.
So anyway, suppose I do fill the tank and turn on the pump..... 1) if I can't hear it that would be a waste of time and effort but I won't know until I try and 2) how do I empty the tank again once my experiment is finished? Do I just keep the pump on? How will I know when it's empty? Won't I burn out the pump if it runs out of water and I don't know it?
I went out and got UNDER the trailer. What I found was that the floor area that is getting wet is "near" where the previous owner installed the new light fixture above the area where I empty my tanks. (From the inside of the trailer, it's inside the upper far left corner of that bathroom cabinet - sort of above that washcloth under the black pipes in the picture of the floor markings.) I thought the water might be coming in from there, running inside the wall and then inside the floor where I have it marked. Thing is, that outside lamp looks pretty well sealed and those wet spots were showing up 24 hours before the rain started.
UNDER the trailer it appears this problem area is between the black and gray tanks but closer to the gray tank and POSSIBLY inside the gray tank area, or at least partially inside. Now... I normally have the gray tank valve open so it constantly drains. (My stupid indoor indication says its 3/4 full when I know darned well it's empty because the valve is open so I have to figure out what the heck is wrong with that too.. and the indicator doesn't work at all
for the black tank either which is a bit unnerving - the whole thing worked great at the dealership when all tanks were empty before I bought it.)
Anyway..... on the day the floor was showing these new wet spots, that gray tank was PRESUMABLY full (I wanted to flush the septic line after I empty the black tank so I was storing the water for that purpose - I do not have a spare hose to flush it any other way, generally I fill the black tank once or twice to rinse it then empty the gray tank to flush the rinse water down - probably overkill but that's me
I'm wondering if the gray tank being full could have anything to do with it.
Today, with the gray tank valve completely open (and the indicator still telling me it's 3/4's full) the area in the circle where it was darkest (above the date I wrote in there) is gone; only the other two "damp" spots are visible. The skin on the bottom is in really good shape and it is fiberglass so I can't imagine it getting wet from underneath but I don't really know. I also noticed that the area along the edge of the tank (under the trailer) is "soft" when I pressed on it with my fingers. This is turning into a real nightmare.....
So.... all that being said, any other possibilities you can think of? I really need to get my hands on a saw and cut that top off in the bathroom to see what's going on in there... maybe that will be the only way I can figure it out?????