Hello James, I think is a very risky bussines to waterline your lssc. In my diorama I put the all boat on the water, and I used too poliester clear resin... (2 kgs). If you want to save the expensive resin you can make a base of natural cork, and make a hole to put the boat at the precise measure; itīs easier and less risky than cutting the boat to be waterlined.
Of course, you can send an e-mail if you need any information about my diorama and my experience with the resin.
A web with a step by step diorama with lssc and seals is
The only problem is the korean language, but itīs a quite interesting web.
Good luck, and send pictures soon.