From the top - it is now nigh impossible to get a car radio so that a fitted unit can be replaced. As many cars - especially EV - have changed to an' Infotainment' unit (how I hate that name!) that is functionally part of the vehicle computer system and includes a radio (albeit FM and DAB only) the market for car radios has all but disappeared.
In our last two caravans (2 berth) we have only fitted the carpet between the front seats. For the remainder of the floor we have put down (pre-used) dark grey rubber-backed matting that you often walk onto when you enter an office block or (some) shops. It is usually branded Initial, and we got ours from an outfit on line called Splendid Pets - they call them 'Dirt Trapper' mats. The good bit is that they can be washed in a machine, they are warm under your feet, easily vacced, and you don't have to worry about muck on the carpet.
Most vans have a plate that houses a 12V 'cigarette lighter' socket with a TV aerial socket in one corner. I either replace the socket with a screw-on F-type (as used on satellite kit) or replace the complete plate so that it has two sockets. The F-type on the plate is actually a double ended socket held in by a spring washer and nut which means whichever route is chosen dis and re connection is simple and quick. The benefit is that F-types give better and more secure connection and will better withstand free cable tension between the socket and TV. Notice that most modern vans now use aerial amps that have native F-type sockets for the same reason. The double socket also gives the option of installing another external connection where a pillar signal or a satellite dish can be directly fed in to the TV leaving the fitted aerial amp to be used for radio - if you have one.
Finally our latest caravan does not have a radio but comes with a Bluetooth connected amplified speaker so that you can play music etc through it from your phone/tablet/laptop. This gives you the option of either feeding the speaker unit by cable with headphone audio from the TV socket (if it has one) bringing the source nearer the listener, or by fitting a low latency* Bluetooth transmitter to the TV. If the speaker does not have a cable connection and you prefer that method just get a speaker that does have a cable socket. I got one (Anker) from a Cash Converters for £10 and it works a treat.
*Low latency means such as Bluetooth V5 which has almost no delay on the audio and you thus gives almost zero transfer delay such that the sound and picture stay in sync. Cable connection does not suffer latency.
