What does the 4800J rating mean for my RV?

It is the surge energy the cord's varistors can absorb before they degrade. Higher is better, but it is not the only number that matters; clamping voltage and response time also count, and VEVOR does not publish those.

Will it fit a standard 50 amp campground pedestal?

It is a 50 amp, 125/250V cord, so it matches the NEMA 14-50 style outlets common at 50 amp sites. Check your rig's inlet and the pedestal outlet before you buy.

Can I use it on a 30 amp site?

No. A 30 amp pedestal uses a different outlet and a 50 amp cord will not plug in without an adapter, and the rig still draws what it draws. Use a proper 30 amp cord or a dogbone adapter rated for the load.

Does the surge protection wear out?

Varistors degrade as they absorb surges, and this one is built into the cord, so it cannot be swapped out. Treat the cord as consumable protection over time.

Is it long enough to reach from the pedestal?

Length is not listed here, so measure the distance from your rig's inlet to the pedestal before ordering. A short cord plus a separate extension is often more flexible.