Very simple, cleaned out what was remaining of the old rubber feet and just pushed these in. I didn't bother glueing them in as I didn't feel they would fall out. If they do, I'll go out and obtain the glue that is mentioned by others in this thread. Very satisfied.
One of the pads on the bottom of the grate kept falling off.
I was able to order the part I needed. The faulty pad had a broken stem.Several pads came in a bag so if I have the problem again I will have the parts on hand. I bought some RTV glue suitable for items at high temperatures; used a probe to make sure the hole in the grate was clear and clean and glued the new pad in place.