12-days road trip round Iceland in a motorhome is convenient. However, do take note of the hidden cost which is the propane gas canister used for cooking and heating water and the car.
Also, though campsites might claim to be open all year round, some facilities might not be open such as water for motorhome and showering facilities. By open, they usually mean that there will be an employee heading down at a designated time to collect the cost of accommodation from you.
Many campsites are closed during the winter because the weather cannot accommodate a motorhome eg water pipe might burst if not turned off. Weather conditions especially wind speed and icy road conditions do not favour the size of a motorhome making such a choice of vehicle very restrictive in terms of diversity of activities available. This is despite the use of winter tyres.
Thus, in winter, a 4×4 vehicle is a better choice as it allows you to go onto a variety of road conditions despite the harsh and unpredictable weather conditions hence giving you more options.
Another option to cater to those who would prefer to have a toilet with them on-the-go considering the long roads would be a smaller camper-van that has a composite toilet and bed with a camping gas stove for cooking.