On my previous tires, Hoosier 31-16.5 QTP's I ran tubes and screws. 16 screws per rim, 8 on inside bead, 8 on outside.
Here's an interesting deal. 15 of the 16 screws on the inside of the rims actually broke off. When I removed the screws, only the head and one thread was attached to the rim, the rest of the screw was broken off and stuck in the bead. None of the outside screws broke.
Current tire is a Phoenix Radial Slick, 32-13.6. No tubes or screws.
Put a dab of polish on each to check slip.
Maybe a half inch per side in 5 runs in vegas.
3 runs at Barona yeilded no more.
7 runs at Fontana, with 3 that really hooked good. One side moved maybe another half inch.
The other one moved 4 inchs or so. I'm thinking I'll go ahead and screw them down.