Having a top on the jacuzzi is the best way to trap heat inside. depending on the size of the jacuzzi, a s olid insulated cover may not work well because of space constraints. Anything that keeps the steam inside works. A poly tarp works ok, if you want to spend a few dollars then you can have a custom cover made from vinyl that snaps or otherwise secures in place. In the summer months i did not use a cover. In the winter, i needed a cover because the water vapor produced by the jacuzzi would fog my windshield up so much that i really needed windshield wipers on the inside. Alternatively, i had a full time squeegy girl when/if i used the jacuzzi while driving during the winter.
A cover also significantly reduces the amount of water that sloshes out of the jacuzzi. which brings me to the second problem you will likely face: Water sloshing out of the jacuzzi while driving.
I tried several methods, including various covers, removable baffles, etc. I ended up deciding that the only solution that made sense for me was to remove about half the water before driving. I plumbed in 55 gallon drums behind the jacuzzi to hold this water. I used a small 110 volt pump and a few valves to transfer the water back and forth. For hoses, i have used 1 1/4 ? cheap plastic flexible hose designed for sump pumps and sold at home depot. Later, I used the more expensive flexible pvc hose like the ones your jacuzzi is built from. This type of hose is available at pool stores. I used the same 110 volt pump to run the jacuzzi water through the stock filter, as well as through the heat exchanger.
Over the years, i utilized several pumps. I started with stock jacuzzi pump, but decided it took too much power and forced me to use a big noisy generator. Then i tried 12 volt bilge pumps.
They move a decent amount of water with very little current, but with almost no pressure. Then i began using cheap harbor freight clear water 110 volt pumps.
These worked quite well, but if i were to build another bus, i would use a pump from a boiler like this: