So garages worry me as they are not as insulated and people tend to not pass by and check in the garage as much so I’ve heard horror stories about small mammals dying in garages.

Apart from that, xpens work great! i use xpens for two of my rabbit pairs and havent had any problems. I’m not sure why you’d use pvc.

If you plan on using your garage you should pad the flooring with soft material like fleece. Concrete is harsh on your bunnies foot and could lead to sores. Since your bunnies are biters i would place a plastic mat on the ground first then cover with a couple layers of fleece for easier maintenance.

I know draughts are a issue with garages which are a issue for buns living in them as the draughts are always worse on ground floor. I would check if for draughts and seal where you can or build your enclosures off the floor abit.
Concrete can cause sore hocks and it an bs really harsh for them and cold so I would either do a elevated floor and lino it or have plenty of areas in the concrete floored pen where they can be off the concrete ( fleece blankets / wooden ledges / wooden hideaways )

I think as long as is not draughty and you have plenty of areas off the concrete and check their hocks regularly you should be ok but may be best to search the net for others examples and what they found worked and didn’t work when converting their garage for bunnnies