Welcome, Bob! My 1995 13' Scamp
has the same issue, soft floor under water tank, hasn't rotted through or anything, but I want to stop it before it does. I don't understand the part about the electrical
tape and larger hose, if it was just going over the male fitting I'd just clamp it, or at most use a food-grade silicone and a clamp.
The lexan and PU glue would make it easier to clean the bottom of the compartment, but if water gets in another way it will hold the moisture in the OSB. A couple spacers might allow air circulation.