Surge protectors are usually rated in joules, which are a way to measure energy, and in essence, the more joules the better. For computer systems, 1,000 joules or more is recommended. This joule rating gives you a sense of how long the device can protect against surges and spikes.
Most commercial motor vehicles in Wisconsin require a USDOT Number and it must be provided at the time of registration. If you are required to have a USDOT Number, and cannot produce the number for verification, your vehicle registration application will not be processed until a valid number is provided.
If a vehicle has a USDOT number, and operates in California, there is no requirement to also show CA number lettering. HOWEVER, you must be prepared to show your CA number papers at the truck stops if asked. Therefore, it is easier on your drivers if they already have the CA number on the doors. Depending on how your truck is used, you may also need MCC (Motor Carrier) numbers and GVW (Gross Vehicle Weight) numbers on your cab doors.