2nd Battery mount options

I have a dual battery kit. Been looking at trying to custom mount in the engine bay or frame mount. Recently have had some work done by dealer. They did not like all the wires I already had. Said I could remove and reinstall or they could work around it and charge extra for all the additional work.

I have seen a few bolt on frame mounts for under the truck. I am going to go with an AGM battery most likely. They are heavier. Thus have been concerned about finding a heavy duty mount to the frame rail. Bolt on. I do not want to weld.

What have others used to mount batteries to the frame rails or is there an ideal spot other than frame mount under the truck?

I actually would prefer to mount in the engine area, passenger side. Easier to work with when running wires. But when the truck needs work, it is in the way. I have seen a few dual battery kits with a lot of relocation of items to get it in the engine bay. Not for me, however, if there is an aftermarket battery mount for the passenger side, I would use that most likely.