Thanks for he replies everybody. Sorry I haven't posted back on this thread in a while. I went ahead with the build despite my hesitations about the silicon sticking to the lexan. It ended up turning out great! I have been using these lids for 4 months now and the silicone is holding very strong.
Here is a picture to show the joint I made on the lids. Normally the light sits right behind the hinge and you can't see it at all.. I just moved it back for the picture.
I love these lids they are very low profile and IMO don't detract from the rimless look one bit. Also the lexan dosen't bow like acrylic does which is nice. No more worrying about top offs or jumping fish.
If anyone is interested in building these let me know and I can show you the exact silicon I used. It does say that it is 100% silicon meant for lexan