Don't plug a surge protector into an extension cord.

I wouldn’t. It’s a fire risk, plain and simple.

Extension cords aren’t designed for the constant load of a surge protector plus multiple devices. They’re meant for temporary, single-device use. The surge protector can draw more current than the cord can handle, especially if the cord is long, thin, or coiled. That heat buildup is what starts fires.

Also, you lose the whole point of the surge protector. A surge needs a low-impedance path to ground—extension cord adds resistance. So your expensive electronics get less protection even if the cord doesn’t melt.

If you need more reach, get a longer, properly-rated surge protector cord (like a 6-foot or 10-foot one). Or move the electronics closer to the wall. Don’t daisy chain safety devices.

Your house is not worth the six bucks you saved on an extension cord.