Sun tubes consume between 55 and 300W depending on the size and length so it would be difficult to run them from an invertor without constant battery changes or the vehicle engine running.
Jackrabbits suggestion is the best one, and these are the type used on Mains hook up for Caravans although remember that if the vehicle is parked outside then you need to ensure that the sockets you use are IP rated at 55 or ideally IP65 and that everything is earthed, correctly fused and a RCD is fitted at the house end of the cable. Also make sure that where any cables pass through the body work, that you fit grommets and the cable is well protected throughout to stop it rubbing against the metalwork.
It is now illegal for unapproved individuals to wire fixed installations in Gardens but this doesn't apply to temporary installations such as extension cables, so if the arrangement is a plug / socket extension lead type then you wont fall foul of the new laws. However, make sure that whoever does the job knows what they are doing and that the installation is safe and waterproof. I recommend the use of either armoured cable or at the minimum Arctic cable for this sort of application.
This sort of extension cable arrangement is what you need to look atAlways fit the socket (Female) connector on the extension cable carrying the mains from the house and the Male (pin) end of the connector to the vehicle. I can't stress this enough. This means that if the system comes adrift or somebody unplugs it with the mains still on, that you wont have three live brass pins to touch!!!.
Mount the Suntube(s), as low down as possible since heat rises

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