MMC:

The OP asked about standard Edison Screw Base replacements for a 12VDC
system. The 'G25' LED cluster that you're having trouble with is a
120 VAC device described as a 'Traffic LED' that is recommended for
"Toll Booths, Receiving Docks & Beacon Warning Light(s)." Why would
you use this as a 'reading light'?

There are many examples of both 12 VDC ad 120 VAC LED clusters with
screw bases at the LEDtronics site in the $25 - $55 range. Still high
compared to standard incandescent bulbs, I agree. But given 10,000 -
100,000 hours (claimed) operation, coupled with very low power
consumption, a couple of them in the OP's V-Berth may be both
practical and affordable.

MW