The way to make aluminum surfaces non-conducting is to have them anodized. Type II and Type III anoziding are non-conducting, however Type 1 is conducting.
However anodization is a surface treatment, so if you tap it and then thread it and put a screw into it, it still will conduct. This is not wise in any case, because anodization converts the top several mils of surface into aluminium oxide, (sapphire or carborundum) the second hardes materaial around and it will dull tool bits and taps and therefore all machining must be done before anodization.
A word of warning. I have designed electronics packages to survie 4,000 G crashes into the playa and 20,000 g gun launches so I have a bit of experience here. Electronics mounted on stand-offs is not recommended in high g environments because the stand-offs can break because they alone carry the g-load of the circuit board. It is much better to use milled channels (slot) on vertical edge guides and mount the circuit board in slots directly on the bulkheads. They can't break this way.
Large capacitors should be epoxied to the circuit boards becasue they will break their leads if that's all that's holdiong them in place.
Bob