These avoidance techniques may be obvious, but I'll mention them just in case...
- Keep your bags as far from bed as you can. In a private room, storing it in the shower is the safest (although I understand that sounds crazy).
- Have a large trash bag, and store your backpack and gear inside while at the lodging.
- Isolate all your sleeping gear (pajamas, sheets, sleeping bag) within your pack. Store them in a sealed plastic bag, and if possible, a physically divided section of your backpack.
I got bed bugs two nights on my Le Puy to Santiago Camino (70 nights). No one else I know got them. Just my luck.
That said, even though I'm really sensitive to all bug bites (including bed bugs), it was a little annoying but not terrible. I used anti-itch creme and took anti-histamines, and it wasn't that bad.
I think people are more fearful of bed bugs than they need to be. I've been bitten by them four times in my life (twice at American hotels), and twice on the Camino, and it's really no worse than mosquitos, if you are careful not to carry them with you.