My wife and I bought a house and the previous owners had installed a plastic liner along the walls of the tub rather than tiling. We've recently started having issues with the caulking around the base cracking. When I started pulling out the old caulk, I found that the liner did not extend down to the top of the tub. We have about a half inch gap we need to seal; the previous owners seemed to have just packed it full of caulk and hoped it held. I could really use some advice on how to seal up my shower.