Well done Steve, great result.
Interesting about the fluid to use in the box, so much so I looked it up and you are dead right about propylene glycol
For others here is a response to the question direct from Airmar:
What type of liquid do I use to fill my in-hull tank/base?
Non-toxic propylene glycol (RV antifreeze/coolant) should be used to fill an in-hull tank/base.
M260 tanks should only be installed with fiberglass resin, Marine-tex epoxy putty, or Fusor T10 EZ. On our newest tanks that have "gf nylon" printed in raised lettering on the sides, 3M's 5200 may also be used to adhere the tank to the hull.
The P79 base may installed with silicone sealant, fiberglass resin, 3M's 5200, or Marine-tex epoxy putty.
NOTE: Do NOT use mineral oil to fill a tank that is secured with 3M's 5200. Mineral oil may weaken the bond. Only use non-toxic propylene glycol (RV anti-freeze) when using this adhesive.