While sanitizing my fresh water tank recently I noticed that the two holding tanks were 'sagging' between their supports. The polyethylene(?) tanks on my 94 Monarch are suspended above the compartment floor by a pair of angle iron straps hanging from threaded rod. There is no solid floor between the two angle iron hangers, the plastic tanks just bridge the distance. The bottom of the tanks appear to belly out whenever there's anything in them. They don't appear to leak or have any other problems but it just seems like a poor install approach. I can just imagine how much fun it would be if one of them were to fail suddenly at a campground or on the way to a dump station.

I'm thinking of trying to back off the threaded rods just enough to allow slipping in a piece of ¾" plywood to help support the bottoms of the plastic tanks.

Does anyone else have holding tanks installed in this manner? If so have had any problems with them or tried to rework the mounting somehow? Would love to hear what others' experience with tank mountings have been.

Thanks!

Oh yes! My 93 had pop rivets attached to the underside floor aluminum sheet. The outside edge is attached to the 1" steel square tube that is the backing for the aluminum skin. Mine was the fresh water tank under the sofa on the road side behind the driver. I drilled 1/4" holes through the floor and the angle iron from below, installed 1/4" x 2-1/2" stainless steel hex bolts with fender washers under the couch. I was able to drill 5 along the inner edge and use the bolts to pull everything up tight against the floor. I did not have to remove the tank. You will need an electricians drill bit that is about 24" long. A cordless drill is sufficient. At the outer edge drilled out the rivets, one at a time and replaced them, just like replacing the rivets on the skin. I used a floor jack and a length of 2x4 as a lifting support to hold the entire tank in place. The holding tanks were fixed using stainless all-thread and stainless nuts with fender washers on the top side of the floor. A couple were under the sink. You need on fender washer up top and one under the floor. Tighten to hold in place. Then just screw the bottom nut under the angle iron up until it is flush with the underside of th floor. Mine had angle iron in two places and I added two more to stop any sag. Took about four hours to fix.

Thanks for the feedback.

It sounds like your tanks may be mounted different than mine but in any case I'm hoping it won't be necessary to actually dismantle the bottom of the compartment to effect a satisfactory repair.

On my coach the threaded rod (looks like ⅜") appear to attach to the chassis itself or at least from the floor framing near to the chassis frame. Both the threaded rod and the one-inch angle iron appear to have ample strength to suspend the tanks, I just need to devise some kind of floor for the assembly to support the plastic tank bottoms.

My hope is that by backing of the nuts holding the angle iron it will provide enough 'slack' to allow the insertion of a ¾" plywood floor board. I'm sure it will be a challenge to temporarily support the tanks while at the same time somehow slipping the plywood into place but that's what I'm going to try to do.

This brings up another issue that I'll put in a separate post under General Discussion: waste tank drain elevation.

plywood will collect water and rot, You could use steel or aluminum angle iron with the "V" facing up to the tanks and the joint across the steel existing angle iron supports.

Treated plywood will not rot, might distribute the weight better than the narrow edges of the angle. I would be worried about abrasion if the angle edges were not padded in some way.

Keep in mind they've been manufacturing boats from plywood since the 1940s but point taken. I used to have an aluminum honeycomb panel material I found at Boeing surplus some years back...maybe I'll see if I can get my hands on some more of that.

Chuck M. (aka Sneelock)

look here:

http://www.ebay.com/sch/i.html...inum+honeycomb+panel

Yeah I looked there, alibaba, aliexpress and a few other domestic suppliers. You'll notice none of the ebay offerings are longer than 4' unless you're prepared to spend $900 or so.

Anyway, there are a variety of honeycomb core materials - it doesn't have to be aluminum or even honeycomb for that matter....just something with a relatively high stiffness to weight ratio. That's kinda why I was thinking plywood to begin with.

Thanks for the feedback everyone. I probably won't start with this project for a couple weeks yet. Will report results.