You can go the bulb method, or you could do something custom.
The advantage with the custom method is you get more light output for less dollars. You also get to choose the color temperature of you LEDS to get light that you prefer. Of course the downside, is cost and complexity.
Here is an article I wrote a few of years ago when I changed my LEDs in the RV (very similar in a boat).
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Now a days, there are better options for LEDs and many of them can forgo the driver board (although adding a $2 board can help the LEDs last longer). You want to look for LEDs with a color temperature between 2700-3500 for warm white. That color temperature is going to be very close to incandescent lights. Many people are starting to prefer LEDs with a color temp between 4200-4500 now. 4200-4500 isn't stark or blinding white, but much more white than warm LEDs. It has a much more modern appearance.
Personally, I would choose COB based LEDs these days as they have better heat dissipation and should have a longer life. They are sold in different sizes with different light output. I would look for an LED with over 200lm if in a double bulb fixture, or over 350lm if in a single
bulb fixture. Pair them up with a cheap
Buck board to smooth out the voltage and you should have a nice light that will last the rated 50K hours. Here is a couple of ebay links.
High Quality LM2596S Power DC DC Buck Converter Step Down Module 5V 3A LM2596 | eBay
COB White LED Light Source Interior Exterior Lamp Chip DRL Fog Light 12V 1 8W 6W | eBay
Of course.. You could always go the bulb method.. Something like this, but you won't get anywhere near the rated life without a board in front.
T10 Wedge Base 12SMD 2X Ultra 2 9W Disc LED 12V AC DC Replaces 25 30W | eBay