5A is pushing it. I don’t push my SST-20 LED’s past 4.5A for turbo runs. At 4A you will be safe.
The SST-20 is in the 3535 (3.5 x 3.5 mm class).
Get the TIR optics from Yajiamei. They fit the 3535 LED’s perfectly and give a good beam. I suggest you get the 10, 15 & 20 degree optics.
LED lens Diameter 20mm Bead surface(10 15 20 25 30 38 45 60 85 degrees lens) XPE/XPG lens ,XP-G2 Lens
https://s.click.aliexpress.com/e/eG0qpt1W
No need for a gasket.