While cleaning the mildew from caulked joints in our plastic shower surround, I noticed that there is movement where the surround wall meets the shower base, and the old caulk isn't holding. I stripped the old caulk out, and I can now push the lower edge of the surround wall about 1/2 inch inward. It appears that water may have leaked back there. I don't hear any cracking or feel any sponginess once it is pushed back to the extreme, presumably against the sheetrock. Is there any way to stabilize the surround against the wall without tearing it out to reglue? Specifically, is there any kind of material that I can squirt into the joint that will percolate all around and fill the space, and that will become firm enough to serve as a posterior support. I'm familiar with the spray foam, but don't think that there's enough room to work it in. I don't want to merely caulk it again, as it will surely leak after some time. Or do I need to take the surround out and reinstall it? Thanks in advance.

I am installing a [url=http://www.mustee.com/durabase/neoangle.shtml]mustee 36” neo angle fiber glass shower base[/url]. Due to the drain cup that protrudes from the bottom of the shower pan and the fact that I have a very shallow drain in the concrete slab, the drain cup bottoms out on the p-trap when I set the shower base in place thus causing it to wobble and not sit correctly. I have determined that I need to build up the floor underneath the shower base about a half an inch. What is the best method for doing this over an existing concrete floor? I don’t want to build up the entire bathroom floor, just under the shower. I have considered using a tile backer board such as [url=http://www.jameshardieeu.com/install.html]Hardibacker[/url] but am having second thoughts about it. I have also considered building a temporary form around the shower base and pouring in some type of self leveler or floating in concrete. Any help would be greatly appreciated. Thanks