$hitty situation for me

Yes it is vented. Most people use foam board, which you can get at Lowe's or Home Depot, as water resistant insulation. Use the 2" board.

It's coroplast, not chloroplasts. You might be able to buy some from a sign shop.

As far as the vent for the tank, check in the nearby closets located over the tank. It is common practice to run it up through them in one of the 4 corners. It is usually 1-1/2 inch black ABS pipe.

Look on the roof above the area of the black tank for the vent pipe coming thru.

p.s don,t wear your sunday suit when working on it, good luck ,you might want to do a major flush and empty before you take things apart. if the vents in a easy spot cut it and fix with a rubber sleeve.

The black tank vent will most likely be on the roof. It's a tube that runs from the tank to the roof and will have a cover with a gap between the top of the tube and the cover to allow venting of the tank while preventing rain from going into the tank.

IF it is a hole.. GOOP works fairly well. Sticks to most everythign LIkewise Eternabond and on a different part of the MH I'm trying Flex Tape (NOT long enough to comment yet.. NOT a water tank of any kind).

IF it is the gasket for the vent pipe.. Well. that ... in theory.. can be replaced.

I have used Plasti-Mend on two different friend's RV's black tanks with excellent results.

Thanks for the link. No current problems but nice to have a product source in a problem does occur.

Black tank work is no fun at all. My 5er has the electric Waste Master system & I have had to replace the valve at the tank. Quite the job.

I would not worry about replacing the coroplast. Cutting it is an accepted method of gaining access for repairs, it is how the dealers do it. They even make a special tape for patching it up.

Not fun taking down the coroplast. Did it in a CG last year after the toilet decided to overflow during the night and soaked the insulation.

I would cut out only what's needed for access and slide it out in one large piece. Cut it left/right direction, not fore/aft. The sheet is unlikely to be a long single sheet and you may be able to remove screws that the factory used to join adjacent sheets and slide it out in one large section. You could add a piece of angle iron or aluminum between the I-beams to screw into.

There is RV "Scrim" tape for use on coroplast and Darco fabric or Gorilla tape is an alternative. Scrim tape is a lot thicker and has a backing on it that needs to be peeled off. Not sure if one is superior to the other. Both stick like snot to fingers, itself and anything it touches!

The insulation they use is batt type fiberglass. Not a good choice for a location like under a trailer. The slightest amount of moisture in batt insulation in it or compressing it greatly reduces the R-value. It definitely gets compressed between a holding tank and coroplast. You can buy rolls of batt insulation at building supply places or Ace hardware. Rigid foam insulation would be a better choice but harder to install.

A leak from the black tank could be from a number or reasons and you need to get full access in there for an inspection. If it's the ABS piping, that's easy to repair but if the fitting to the tank, that's harder to deal with and at worst, could require tank replacement. It might be something a simple as a coupling that wasn't properly glued at the factory.

Depending on where the leak is and where water travelled, water could potentially be outside of the I-beams where the outriggers are and you may need to slice the Darco fabric to get at the insulation.

While you have the coroplast down, it could be an opportunity to do other work under the trailer like wiring, adding an in-tank sprayer (if not so equipped), installing Horst Miracle probes, etc.