suggestions for mounting a thule bike rack on/in the bed area?

howdy kids. i need some mechanically sound ideas for mounting a thule rack in my '02, double cab, sr5, 5' bed. she has the factory bedliner (not the spray-on type), the u-brackets near the corners (midway up the walls), and no factory roof mounts. from my old vehicle i kept the thule towers (clamp action for a roof rack), the crossbars, and the two full-length, one piece trays. on the trays, it's the alligator type clamp (up front) spaced for disc brakes. i've seen the fork clamps that attach to the floor of the bed (or on a 2x4 piece of wood), or on the lip of bed, so the bikes run transverse to the bed. don't want to go that route; rather, i want to use the aforementioned thule trays and crossbars if possible. does any body know if there are grommeted holes on the bed floor hidden by the bedliner i can use to attach my existing equipment? on some american trucks i've seen a metallic tubular piece of metal that attaches lengthwise on the lateral "lips" (top part) of the bed where one can use clamping towers and really long crossbars. does toyota make one of these tubular pieces of metal? my buddy is a competent m.i.g. welder if that helps, and i wouldn't be against drilling into the bed either. i'm guessing though that the sheet metal's pretty thin and i might need to reinforce the areas i drill. i would like to make the towers and crossbars a permanent fixture (i.e. relatively thief-proof, or at least a major pain if they wanted to liberate my shizzle). thanks.