I used Unirac mounts, all aluminum. Anything to weld or permanently fix them in place also prevents me from roof repairs, etc., and would more or less destroy the racks for re-installation. The rails/mounts were roughly 10% of the total cost of my installation, not trivial.

They are located right above the garage and face the street...it really would be a bold move on a thief's part to hijack them, but who knows.

My father-in-law's Toyota truck was hit here in Sacramento about 8 months ago...welding bolts on the converter wouldn't do it as they use ratcheting pipe cutters...three minutes, tops, to sever both sides.

speaking of bold

i keep & ear out[out of sight in the summer] for a neighbor's place for sale- a year + now. i recently heard a big truck working over there & listened carefully & could tell was a big wench type truck picking up a propane tank, so i thought was legit; they stole it 1/2 full of propane.

Solution to catalytic converter theft:

Get a piece of hardened or wear plate steel (manganese alloy) from a metal fabrication shop, maybe 1/4" (0.75cm) by 1" (2.5cm) about 36 - 42" (90 - 110cm) long (long enough to follow the pipe where it passes above the cross frame. Have the muffler shop MIG weld this bar to the exhaust pipe in front of and behind the cat. converter.
Manganese alloyed steel cannot be cut with any pipe cutter or saw, it can only be cut with a cutting torch or abrassive cutoff wheel. Using the later to cut throught the wear plate steel would take 5 - 10 minutes and create a lot of sparks and noise. Most thieves need to be in & out in less than 3 minutes without creating any sound.

"Solution to catalytic converter theft:"

but would it protect against rsb's ?