I doubt it's too late. Something to bear in mind with Rally GB is the area covered by the rally and the amount of time it takes to get around. Play around with Google Maps to appreciate journey times and arrange accommodation accordingly. Also be aware of the way stages are accessed here. Usually an official 'car park' will take the form of accessing a forestry track that'll take you up into the forest to the stage. The 'head' of the car park will be at or very near the stage, but will start filling up from the night before, meaning that if you arrive late (an hour or two before the stage starts), depending on the stage, you could have a steep walk of up to an hour to just get to the stage!