Invisible collision brushes & meshes
Just a word of warning. The current version of AztecaLite uses invisible collision hulls for the INF vehicle meshes, which is the reason they don't show up online. Some kind of odd UT netcode thing w/ mesh actors & BSP collisions. Though I used solid (non-hollow) brushes. May work w/ hollowed-out ones, where the meshes aren't in any "solid space". Don't know, just make sure you test it online before releasing the map. Big mistake not to have done that w/ AztecaLite on my part...
Easiest thing to do would be to use "blockall" actors, found among the keypoint list. What you do is set the top view & one of the side view viewports to show actor radii (right-click on the viewport bar and select "Actors --> Radii View" in the pop-up menu), then add maybe 3 or 4 of the blockall actors, setting all their collision properties to "True", and adjusting the collision radii & heights to match the mesh dimensions (using the veiwports w/ the collision radii showing). Done right, it can be just about as good as using invisible collision brushes, but you're 100% guaranteed it won't bug the map out online.