If you are too lazy to do your own)

My types.xml

<types>
<type name="vg7_poseidon">
<nominal>0</nominal>
<lifetime>172800</lifetime>
<restock>0</restock>
<min>0</min>
<quantmin>-1</quantmin>
<quantmax>-1</quantmax>
<cost>100</cost>
<flags count_in_cargo="0" count_in_hoarder="0" count_in_map="1" count_in_player="0" crafted="0" deloot="0" />
</type>
</types>

My spawnabletypes.xml

<spawnabletypes>
<!-- POSEIDON -->
<type name="vg7_poseidon">
<attachments chance="1.00">
<item name="RFWC_Anchor_Rope" chance="1.00" />
</attachments>
<attachments chance="1.00">
<item name="SparkPlug" chance="1.00" />
</attachments>
<attachments chance="1.00">
<item name="TruckBattery" chance="1.00" />
</attachments>
<attachments chance="1.00">
<item name="HeadlightH7" chance="1.00" />
</attachments>
<attachments chance="1.00">
<item name="HeadlightH7" chance="1.00" />
</attachments>
<attachments chance="1.00">
<item name="CanisterGasoline" chance="1.00" />
</attachments>
<attachments chance="1.00">
<item name="EngineOil" chance="1.00" />
</attachments>
<attachments chance="1.00">
<item name="FishingRod" chance="1.00" />
</attachments>
<attachments chance="1.00">
<item name="FishingRod" chance="1.00" />
</attachments>
<attachments chance="1.00">
<item name="FishingRod" chance="1.00" />
</attachments>
<attachments chance="1.00">
<item name="FishingRod" chance="1.00" />
</attachments>
<attachments chance="1.00">
<item name="ADM_Divingtank" chance="1.00" />
</attachments>
<cargo chance="1.00">
<item name="Wrench" chance="1.00" />
</cargo>
</type>
</spawnabletypes>

My events.xml
I just added him as a child to the RFWC.

<events>
<event name="VehicleRFWC_Watercraft">
<nominal>10</nominal>
<min>0</min>
<max>10</max>
<lifetime>172800</lifetime>
<restock>0</restock>
<saferadius>500</saferadius>
<distanceradius>100</distanceradius>
<cleanupradius>200</cleanupradius>
<flags deletable="0" init_random="0" remove_damaged="1"/>
<position>fixed</position>
<limit>parent</limit>
<active>1</active>
<children>
<child lootmax="0" lootmin="0" max="2" min="0" type="RFWC_Whaler" />
<child lootmax="0" lootmin="0" max="1" min="0" type="RFWC_CarpBoat" />
<child lootmax="0" lootmin="0" max="1" min="0" type="RFWC_CarpBoat_Rusty" />
<child lootmax="0" lootmin="0" max="3" min="0" type="RFWC_Zodiac_Orange" />
<child lootmax="0" lootmin="0" max="3" min="0" type="vg7_poseidon" />
</children>
</event>
</events>

The coordinates of spawn points can be taken from your own or borrowed from other boat mods and added to your own cfgeventspawns.xml
With these settings, everything works and appears, Poseidon slots will have everything you need except the left and right doors, until I added them to spawn, because they are non-functional.