Series Land Rover (UK/Europe)
Serving the Series I, Series II, Series III and other Land Rover communities worldwide.

Well King Canute never managed it with the sea, but we can at least try with a Series Land Rover!
You may not wish to visually modify your vehicle as much as in the photo above. Personally speaking, I don't do cold!

There are two aspects to keeping the weather out of a Series Land Rover; firstly, reducing cold drafts to a minimum and secondly keeping what ever heat the standard heater struggles to produce inside the vehicle for as long as possible.
Drafts go unnoticed for most of the year so they can only really be sorted out once winter has arrived. The door seals on early Series Land Rovers are a very basic design and tend to be hard and harden more with age. So gaps between a door seal and the edge of a door are common. One approach is to use self adhesive household window/door seal fixed to the door itself so that seal contacts seal. The seals are available in a range of thicknesses. Alternatively, the more flexible and more effective door seals from the Defender Land Rover can be used, but the metal lip on the Series Land Rover doorseal mounting flange has to be ground off to allow the different design of the Defender seal to be fitted.

All Series Land Rovers have horizontally sliding windows and there should be a thin rubber seal mounted on the non-moving pane to block out drafts (and rain!). With time, these seals perish, harden and even break up. They can be replaced, but the metal guard on the window's edge has to be removed and this is usually not easy. An alternative is to find a suitable sized thin rubber channel that can fit over the edge of the window to fill the gap but still allow movement of the window.

Basically, the Series Land Rover is a metal box that loses heat like a sieve loses water. Wherever you can add heat insulating material to the metal surfaces then the wamer your driving environment will be. Carpeting and closed-cell insulation on the floor helps a lot, as water spray conducts a lot of heat away from under the vehicle. The sides and door interiors can also benefit from some sort of heat insulating material adding to them. You can stuff some loft insulation between metal surface and interior panels, or another cheap alternative, is to use closed cell polystyrene ceiling tiles cut to size and added in layers where required. Don't forget under the roof lining.
Traditional elephant hide style seat covering does nothing for keeping body heat inside the human body, so seat covers which trap as much air as possible, will help lessen the inital shock to the system on that cold winter morning.
Other points to check, are that the sealant between body panels is still in existence and that the seals around the windscreen vents are still doing the job they were designed for.