This topic is closely related to the request for information on chaffing. I have included a section from Dr Edmund Burke's excellent publication "Serious Cycling". Its relevant to the GVBR because you will be riding in sweaty clothes for 8 days and if you do not follow his advice, you may end up cutting short your ride.
"Saddle sores are posterior skin infections that start life as a small pimple. In most cases the saddle sore’s life span is a few days, but during this time, they may become hard, red, inflamed and painful, In some cases, if the infection doesn’t disappear, it spreads to adjacent tissue and creates large sores, boils, or cysts that affect more tissue and may even require surgery.
To prevent saddle sores, you need to keep that part of your anatomy that everything in cycling “hinges on”- the groin area- clean and as free from friction as possible. Saddle sores usually occur from irritation or chaffing of the hair follicles. The predominant infection, staphylococcus, is forced into the skin by pressure or irritation from the saddle, and a saddle sore is born.
Because chaffing and sweating are major causes of saddle sores, every effort should be made to minimise them.
First, dress right. To control chaffing and cushion your posterior, wear chamois or synthetic-lined cycling shorts. Keep the chamois material soft by ruffing in a washable lubricant such as Chamois Butt’r before every ride. Wash the shorts often. In fact, buy two or more pairs so that you always have a fresh pair. Many companies offer more high-tech and synthetic liners.
Second, wash regularly with an antibacterial soap. Regular use will reduce bacterial growth and the chance of infections. Ordinary soap will not work as well because it does not contain antibacterial agents.
Third, experiment with different saddles. There are many saddle brands and configurations on the market, in gel, leather and nylon. Find one that fits you best, one that is wide enough to let the bones on your rear end (ischial tuberosities) make proper contact with the rear of the saddle but is not too wide. A wide saddle will cause chaffing, which could lead to bacterial infection. A good saddle should be stable enough to keep your body still, yet flexible enough to absorb large road shocks.
Fourth, ride smart. Stand up on the bike periodically and stretch out the posterior muscle for 15 to 20 seconds every half hour. It’s also wise to rise out of the saddle to go over railroad tracks and rough patches. If all else fails and you develop a saddle sore, don’t cover it with salves or ointments because they have the tendency to keep the bacteria alive
Like all great cyclists you will have to deal with saddle sores sometime, but cleanliness, proper clothing and equipment, and skin care may be all that is needed to keep you in the race and not on the sidelines sitting in a comfortable chair."
From “Serious Cycling” 2nd Ed, by Dr Edmund R. Burke, Chapter 5 Staying Healthy and Injury Free.