A technician would use a set of backup wrenches:

The use of backup wrenches is particularly important in situations where damage to connections or fittings may occur due to the application of excessive torque. For propane connections, which are crucial for safety and proper functioning within an RV, using a backup wrench helps stabilize the fitting being tightened. This ensures that the connection is not overly stressed and reduces the risk of damaging the fittings or causing leaks.

In contrast, the other options suggest uses for backup wrenches that don't apply as directly. While backup wrenches could be employed in situations involving odd sizes or when a wrench breaks, those are not the primary context in which backup wrenches are specialized tools. The correct answer highlights the safety aspect associated with using backup wrenches in sensitive applications like propane, making it clear that their proper usage is foundational in maintaining secure and safe connections.