Just throw them in the oven and slowly open them up mate. Using pressure and waiting and if its taking too long or too much force, up the heat a little and wait for five minutes. Then try again.
Starting with low heat makes it easier to not over temp. You can burn the casing.
Polish the side light dome as the glass lenses let rays through that make it yellow.
Make sure you sand the chrome well. Otherwise it can begin go lift the pain when chrome peels after time.
Butyl tape on top of the seal should be fine. A thin layer.
If you're worried about fogging. Fit a 4mm bulk head connector so you can have a kit fitted. It's how I'll have to plug into UK lights as they don't have a bung on the top of the casing. I'm sure the parameters yet for moving air just yet to get it right. But km confident it's just a combination of controlling air movement and secret sauce