By the time its stretched and allow some extra for down in the valley, you will need 32-33mm tape (35mm), you just dont want to tape up the wall as this will fold over and allow sealant down under the tape.
I put a tiny drip of superglue on the end between the tape and rim, pull it super tight all the way around and keep the tension on, de-tension on the overlap, cut the tape into a point and put another little drip of superglue on the end to stop it lifting. The use a heat gun the whole way around pressing the tape in with cloth or gloves as it will be bloody hot.
EDIT: A few weeks back, I built one of my boys a set of DT M502 which are a 30mm internal width, a cheaper version of the EX511, I used 32mm tape on them.
Quick and easy conversion to tubeless: The Tubeless Pro Rim Tape by bc basic After almost 2 years of testing and a long series of prototypes, we finally have a rim tape that meets our requirements. The Tubeless Pro rim tape from bc basic offers just
www.bike-components.de