Hi all,thanks a lot for your nice comments! Squiffy,I started exactly like you with a grass mat on the dining room table and hangar tents made of glue-drenched tissue ...that's about 15 years ago now and I'm still learning a lot with every new project I start.
I think your dioramas are pecfect as displays for your nice models because you can rearrange everything for new sceneries.
Sasho,I used a 1mm thick plastic sheet,Revell aqua color gloss clear,and Acrylic thick material you get in every do-it-yourself market for small money.Don't use silicone, paint won't stick to it.You can see it on the top of the third photo.You could even use genuine Acrylic gloss varnish instead of revell aqua color if you want to do a larger dio ,savesw you lots of money.
Most important is to let each layer dry thoroughly until it 's clear,if it is still milky and you apply another layer it will stay like this forever.
You could also quit with the clear plastic sheet ,if you want bigger waves,and apply the acrylics to a sculpted and painted styrofoam board ,like I did here:


One hint to the colour of water:Do not paint it blue!