Enclosed trailer upgrades. Whatcha got?

Disco lights and pole?

I've got a 18x8.5 and we're in a similar boat... it's car transport, our hotel, our work area, and our kitchen. We did a lot of stuff to it and it's been amazing...

-work bench, vice, parts cabinet, rolling toolbox under the work bench up front: this has been fantastic, the parts cabinet is heavy so it helps keep the tongue weighted. If I were to do it over again, I would make a workbench without legs or get rid of the front center one. Fitting our 735i is an absolute PITA, and not having a leg at the front center of the trailer and being able to tuck the hood under the work bench would help a bunch.

-Power: This took way too many iterations and lessons learned are double whatever you think you need. Start with a big battery, you won't regret going too big. Go bigger on the solar panels than you think you'll ever need. I got a 700W true sine wave inverter and I wish I went bigger.. we got a tiny 1200W air fryer and it'd be nice to run that off the inverter (it seems silly but an air fryer for cooking at the track is amazing). We also have a 2500W generator that's really quiet but I'm trying to move away from it... since we don't use much power, solar/battery/inverter is the way to go and right now the generator is overkill and the solar system we setup is just barely not enough. We also have a tiny flux core welder on board, but 99% of the time we need it we've been able to run an extension cord and borrow someone elses power rather than setup the generator. I recommend solar/battery+100ft extension cord rather than a generator.

-Cooking: we have a BBQ, mini burner, propane tanks, a couple bins of cooking stuff, and a camping kitchen... it's epic when we have crew that's willing to cook, but without crew usually we're too lazy to cook and I have a feeling we'd be happier with an air fryer and 10lbs of pizza rolls for the weekend lol.

-Lights: yes! Everywhere, they've been the best thing to add by far. Get 100ft of strip lighting off amazon and go nuts. Inside, at the rear gate, along the top edge where you usually setup your paddock, under (this looks ricey but it helps a lot when towing at night so you can see where your trailer is along curbs/lane dividers). String lights are better than a flood light for paddock lighting since it doesn't blind you or shadow. We started with a flood light and it would always blind you and was useless for working on your shitbox all night since you'd shadow whatever your working on. Run your paddock strip light across the entire top edge of your trailer and it's perfect.

-On one wall we have parts storage, a tire rack, folding chair storage/folding table storage, EZ up, disposable plates/cups/etc

-On the other wall we have hangers mounted to air our your gross suits, and a mirror for helping suit up

-under the trailer we have 2 tanks: one is a 40gal fuel cell, other is a 40gal water tank, both on pumps. Water runs to a spigot at the front and it gives you running water for cooking, living, showers (I found a $20 RV propane tankless water heater and adapted it inline of our garden hose for hot showers), and it's also saved our BMW twice from blowing a head gasket after overheating.

-For sleeping I know some people like beds that drop down, but blow up mattresses and cots have worked great and wall space has been kinda precious. On one wall I've got a sheet of 1/4" lexan bolted to the wall as a spare windshield which I'd rather have than a weird bed mounted to a wall.

-"Bathroom" ... intake is a funnel which punches through the floor with PVC and exits to the center of the trailer... I think you get the idea. lol. #1 only and for some reason every new guy touches it once before asking it what it is. It's been great for long trips since we tow with a suburban so 5 people and a 9-24hr drive puts us in multiple situations where there isn't a bathroom or a place that's socially acceptable to pee in public.

...I still feel like I'm missing some stuff but I had a lot of fun setting up our trailer and it's totally been worth the investment. Pack dense and high, consider weight distribution, and leave as much parking space as possible. We're able to fit all this crap (and then a bunch of stuff I didn't mention) into an 18' and it will take a miata+pit vehicle, a prelude, or a BMW 735i with the bumpers removed. Sounds like you've got lots of room for activities at 20'!

Pics, anyone?

If they run long enough down the walls (length of the trailer), you can remove the tires, spread the bars farther apart, and then make platforms that sit on top. Thus elevated beds. Then cots or mattresses on the floor, for more people.

And this is not my idea. All roads racing has this setup in the trailer.