[Astro_Bot]

No need for switched outlets at 12V - no arcing or sparking at such low voltage and current, and unused sockets are air gaps, so no power drain at all. Better to get sockets with flip cap to keep out the dew (for corrosion resistance more than anything). eBay sockets are cheap and often include an inline fuse of 10 or 15A - I wouldn't recommend a smaller fuse as it's only short protection you need - there's no appreciable human shock hazard at 12V. Even with 10 or 15A fuses, you might occasionally need a spare fuse - I blow one every now and again.

You can get a bigger battery with more capacity with less space and weight, rather than two batteries in parallel. Just something to consider.

Right angle connectors at the mount stay in better - 2.1mm/5.5mm tip positive is right (as mentioned above).

If possible, get AGM (absorbed glass mat) batteries - they last longer and are typically roll-over and drop proof. With AGM, you won't need a ventilated box and can seal it "permanently" (though you might want to get into it anyway to change a fuse).

Size batteries based on long life, which means not discharging below 50%, though you can go to 60% to "juggle" sizes and capacities without too much harm. If you don't care about long life, then fair enough.

Any other plastic container would be cheaper and probably just as good as a Pelican brand case - "small" battery boxes at eg. Repco are cheap (around $25) and still pretty big. I suppose that's a matter of taste more than anything else.

I've used cheap 240V-to-12V power supplies off eBay without issues, but some people report problems, so check the reputation beforehand. "De-rating" is a good risk reduction strategy, e.g. double the current capacity you think you will actually use.

Just in case you were thinking about it, don't use a normal power supply as a charger! If you get a charger with "supply mode" you may be able to use it in lieu of a separate supply. But keep in mind that "supply mode" won't be suitable for charging, so resist the temptation to wire it up permanently - your charger needs to "sense resistance" from the battery and nothing else to run it's charging program properly. A 3-stage charger is the minimum.

And one last one: don't recharge through the outlet sockets - you'll probably blow a fuse.

Edit: Just saw the last couple of replies - I started typing before they were posted.