Do these bolt directly to the truck without drilling?

Yes — they mount at factory headlight locations. You'll align them where your OEM housings sit and secure them using the existing points. No frame or fender drilling required.

Will the halos stay on all the time or only when headlights are on?

That depends on your wiring setup. Most builders run the halos to turn on with parking lights or headlights. You have flexibility in how you wire them to your truck's electrical system.

What about bulb replacement down the road?

LED halos are solid-state — they don't burn out like incandescent bulbs. If the projector uses a replaceable bulb or LED module, you can access it from inside the housing. Check fitment to your specific truck to confirm module type.