What material do you guys use for this?

I used neoprene. Got it from my local hardware store. Glued two layers together with trim adhesive, then glued them into place on the firewall. Front bulkhead too.

I think the original stuff was felt? Not sure, but it did a pretty decent job of holding water against the tank and firewall. The carpet that some people have used over the years as a replacement did a really good job of holding water.

--DD

Ditto. I used stuff in the window and door insulation display.

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old pc of carpet

Thanks for the quick replies.
Keeping away from the hydrophyllic stuff seems a good idea.

I used furniture pads with adhesive on the back as sold at Home Depot and Lowes. Comes in 4x6 inch sheets.

I used a rubber sheet from the plumbing department

Polyethylene pipe wrap from Lowes, glued in with 3M adhesive. Won't hold water.

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I found some adhesive backed felt at Grainger that is a near perfect match to the stock pads. Item # 2FJA9 . Felt Sheet, F3,1/4 In Thick, 12 x 12 In

Link

Closest is probably felt from the insoles of shoes or as add one for shoes. I like the felt. If you are worried you can scotch guard. In my experience the rust on the inside of the tank is wher the worry is. Maybe line the tank with neoprene? Oh, just kidding Dave, I spect you are right on this one too. I saved the old ones spruced them up a bit and reglued them on. Figure the tank holds them in place.