I have towed many D2's wth my D2's. 5 hr trips frequently. Unless you have replaced the entire cooling system I recommend stopping every hour and checking coolant level. I overheated a Disco once because the heater hose was peeing out of the hose clamp against the firewall. No steam, could not smell it because it never hit the exhaust. 3 hrs in, it had pissed all the coolant out.

https://cimg7.ibsrv.net/gimg/landrov...7efc7a28b6.jpg

Sounds like good advice regardless of whether or not you're towing. Maybe every hour at first, and then extended progressively as you gain confidence during the trip. But all hell can break loose at any point, regardless of whether it is a Rover or any other vehicle.

Doug, you are a brave man.