I've decided to go with expanding foam then silicone it. I'm not sure when I will start it but soon hopefully. I already hit my first speed bump as it's an ex turtle tank the ramp was in it and as I'm turning it up straight the ramp won't be needed, so for about a week I've been attempting to cut it out but failed so today I put turps along the silicone the left it for about ten mins and it came out easy peasy.