Phil,Chapel lane is a long way from the NEC and even in good traffic will take a long time and the route on that bit of M42 gets very congested and has variable speed limits and dozens of speed cameras.Kingsbury is much closer and the M42 that you would use is less busy,if you wanted you could go along the A46 from by the site which is even quieter and you can enter the NEC from the less busy 'back door'
A final choice would be down the back lanes with no traffic at all,I know which site I would pick,but the choice is yours,either way they are both popular so booking early is essential.If you wanted a commercial site there is a lovely adult only site 5 mins from the NEC and next to a golf course and is on the edge of Meriden.