Chargeable lantern like this. I have on my boat, very versatile and useful.
Use a router https://www.amazon.co.uk/TELTONIKA-RUT955-LTE-4G-Router/dp/B017DAJIS4
With a Omni directional aerial
Just insert any 4g dim, Smarty offer great monthly deals
If you get a WiFi enabled TV (LG) you can connect it to the boats WiFi
I've used round foam core bytyl tape (similar to this) for similar situations, it comes in different sizes. You can then trim over the butyl tape.
Another option would be to add a simple rubber gasket along the gap.
That said, /u/AmarulaGold is right about it reducing overall ventilation - if you don't already have adequate ventilation - it might pose an issue for you later.
I've got an old MSi GE62 with a GTX970M (good enough for Factorio, and that's good enough for me). Its a power hungry little beastie. It often takes me by surprise how quickly it can get through the leisure batteries.
Then there's the low power stuff. I use a little portable monitor like this, with a Pi 4 running Retropi and a firestick. Then I've also got the Quest 2 and the Switch, which are both USB C devices. I've got decent USB C car chargers for these and they've got just enough guts to do the job.
I had to run some beefier cables to deal with everything being plugged in at once, especially when you add in a couple of phones and a tablet.
You can almost certainly safely power a 12VDC device from your 12V batteries. The DC voltage will probably get up to 15 or maybe even more when charging but that's not all too different from what your unregulated wall wart that came with router will do. Those cheap power bricks that come with your ho me routers are not very precise.
If you are paranoid or have reliability problems or just want to be 100% sure, you can buy a DC-DC converter.
In either case, you should wire the device to the DC power source with an automotive or marine style fuse block.
example: Powers up to 6 DC circuits: https://www.amazon.com/6-Way-Fuse-Block-Negative-Bus/dp/B07DYT2TVS
Or: 5 pack of blade fuse holders: https://www.amazon.com/MCIGICM-Inline-Fuse-Holder-Blade/dp/B081DHT8Y7
For a 24 W device, I suggest a 2.5A or 3A fuse minimum, you may use a bigger one but do not use a fuse that would allow the circuit (the wire) to melt. 5A or 7A or 10A should be fine with almost any reasonable supply wire.
I love these connectors. solid connection and rated for real loads. You can get them in most configuration and size wire you need.
The previous owner put in those types of sockets. I ripped them out immediately.
If you want the connector to fit nice and tight, only coming out when you want it to come out, use something like a mountable xt60
Want something that comes out a bit easier? SAE connections
There are Anderson plugs, barrel connectors, and even the humble banana plug terminal, to name but a few.
Don’t use ancient lamp sockets unless you’re looking to botch things in on the cheep.
I use a small 12v / 300w inverter to charge my MacBook Pro (40w charger) from my car/campervan and it works perfectly. £30 from amazon. It’s even got 2 USB ports on top of the 3 pin plug. It sounds like it will save you a lot of hassle.
BESTEK Car Power Inverter DC 12V TO AC 230V 300W Soft Start Car Converter With 12-Volt Clip-On Battery Cigarette Lighter Adapter and Dual USB Charging Ports https://www.amazon.co.uk/dp/B008HOECP0/ref=cm_sw_r_cp_api_i_iEb1EbK4574KQ