Ron,
Get some good cam lock belts, Gforce is perfectly good and less expensive than many others from OMP, Willams, etc. and get the clip on set with the belts.
That will provide you with eyelets and clip on pieces that can go on the belt straps so the belts can be cliped to the eyelets. Buy, or make, the load distribution plates that they sell with them - about 3"x3" 1/8" steel. Then, simply bolt the eyebolts where they need to go to mount the belts.
As long as you are bolting through around 1/8" metal or so, you'll have plenty of support. The belts come with guidelines for thicknesses of material needed to be safe, but these guide lines will get you through I think.
If you have a space frame then you can weld threaded tubes to the chassis as Paul describes. If you have the RCR chassis as you do I'd use load distribution plates nad bolt them up. Fran might have another solution, but the eyebolts and load plates will work great and are used in race cars all over the world.
Ron