This does work well Colin, I did the same thing on my Maiami and MTBs' Billings portholes about 12yrs ago, and used UHU glue poured in, with cling film on the back. Got a few small bubbles but you don't notice as the port holes are only around 5mm (no pun intended😁). As you say, allows the lights to show from the inside and keeps water out. For a very clear 'glass' you could use crystal clear Polyester encapsulating resin which is designed for jewelry, insects etc. Costs a bit more but very glass like. I did experiment with cabin sized windows using various resins and glues but got a lot of bubbles, and the std polyester resin was a bit opaque, (still made a nice solid window in 3mm balsa though. - about 40x30mm)
JB

Hi Martin, yes I have tried it, but preferred to hard glaze as the silicone discoloured fairly quickly.
I'm always trying different things as like you I love to experiment to try things out and if they work it's great, but if it fails it doesn't matter as it then means I have learnt something.
Cheers Colin.

Hi Colin,
I do like that idea.
Have you tried clear silicon ?
It might work.

Martin555.