In addition to making a very good ground connection next to the welding area you may also do the following disconnecting/unplugging to keep sensitive electronics safe. At a minimum do remove the positive and ground cables on both house and chassis battery(s), and place the ground clamp as close as possible to the work.
Foretravel Technical Support recommends you disconnect the following before welding on completed coaches:
U240 All of the above except ABS U300/U320 C-E18 Same as U270/U280/U295 plus:
U300/U320 C-E22 Same as U270/U280/U295 plus:
Any coach with Aqua Hot option:
Any coach with Primus option:
Additional Reading:
Welding Checklist
Checklist Question