Q: Airspace underneath pickup?

Quick pickup question: I always hear how it's not a good idea to have an airspace beneath your bridge, which is why a lot of modern bridges have the extra screws to get it tighter to the body, and it's good to have the metal bridge pickup base.
What about the neck pickup? Mine is suspended in a humbucker route on spacer tubing, so there's a gap underneath and all around it.
I've seen pickups with dense foam underneath -- is that a good idea? Better than spacer tubing?

As long as the pickup is secure, I don't think it matters.

Foam is typically used for P90's which don't mount in the conventional manner.

Lots of guitars have had their pickups floating on springs and screws for a long long time and it seems to work.

The extra 2 bridge screws have nothing to do with air space - my opinion. Purpose would be to keep the bridge flat on the wood to transfer vibrations.

I installed an Area T neck p/u into a vintage tele by floating it on a new pick-guard over a HB route and it sounds amazing, very tight defined sound. Wouldn't dream of putting foam into it - sounds a bit acoustic the way it is.

Putting in material that can stop or eat vibrations couldn't possibly be a good thing --- unless you want to lessen feed-back at high volumes, it may work or maybe not.

You can always try with foam and without to see if it makes any diff - but I would keep the pick-up mount the way it is anyways or the p/u may be moving around while you play.